A&P Test 3

Metabotropic receptors

- type of neurotransmitter receptor that contains a neurotransmitter binding site but lacks an ion channel as part of its structure

components of tendon reflex

1. Increased tension stimulates sensory receptor (tendon organ) 2. Sensory neuron excited 3. Within integrating center (spinal cord), sensory neuron activates inhibitory interneuron 4. Motor neuron is inhibited 5. Effector (muscle attached to same tendon) relaxes and relieves excess tension

General components of reflex arc

1. Sensory receptor: responds to a stimulus by producing a generator or receptor potential 2. Sensory Neuron: axon conducts impulses from receptor to integrating center 3. Integrating center: one or more regions within CNS that relay impulses from sensory to motor neurons 4. Motor neuron: axon conducts impulses from integrating center to effector 5. Effector: muscle or gland that responds to motor impulses

Sensory and motor process

1. Sensory receptors detect a sensory stimulus 2. Sensory neurons convey sensory input in form of nerve impulses along axons which extend into posterior root of spinal nerves; can go to three different paths: sensory tract: white matter, posterior gray horn; posterior horn spinal cord reflexes 3. Axons extend into white matter of spinal cord and ascend to the brain as part of sensory tract 4. May enter posterior gray horn and synapse with interneurons whose axons extend into the white matter of the spinal cord and then ascend to the brain on sensory tract 5. Enter posterior gray horn and synapse with interneurons with somatic motor neurons involved in spinal reflex pathways 6. Motor output from spinal cord to skeletal muscles involve somatic motor neurons of anterior gray horn regulated by the brain 7. When activated, somatic motor convey motor output in the form of nerve impulses along their axons, then pass through the anterior gray horn and anterior root to enter the spinal nerve 8. Autonomic nerves send motor output from spinal cord to cardiac muscle, smooth muscle and glands, from autonomic motor neurons on lateral gray horn; convey impulses which sequentially pass through the lateral gray horn, anterior gray horn, and anterior root to enter spinal nerve 9. Axons of autonomic motor neurons from spinal cord synapse with another group of autonomic motor neurons located in the PNS

Crossed-Extensor Reflex components

1. Stepping on a tack stimulates sensory receptors (dendrites of pain-sensitive neuron) in right foot 2. Sensory neuron excited 3. Within integrating center (spinal cord), sensory neuron activates several interneurons 4. Motor neurons are excited (of left leg) 5. Effectors (extensor muscles) contract, and extend left leg

Components of a flexor reflex

1. Stepping on tack stimulates sensory receptor (dendrites of pain-sensitive neuron) 2. Sensory neuron excited 3. Within integrating center (spinal cord), sensory neuron activates interneurons in several spinal cord segments 4. Motor neuron excited 5. Effectors (flexor muscles) contract and withdraw leg

Components of stretch reflex

1. Stretching stimulates sensory receptor (muscle spindle) 2. Sensory Neuron excites- goes to brain 3. Within integrating center (spinal cord) sensory neuron activates motor neuron 4. Motor neuron is excited 5. Effector (same muscle) contracts and relieves the stretching

Biogenic amines

: bind to metabolic receptors norepinephrine , epinephrine, dopamine, serotonin: excitation or inhibition

Reverberating

: incoming impulse stimulates the first neuron, which stimulates the second, which stimulates the third, and so on

Resting Membrane potentials

: is positive outside and negative inside this is determined by Unequal distribution of ions across the plasma membrane. There are more K+ leak channels than Na+ leak channels, so more K+ leak out than Na+ leak in Most anions cannot leave the cell because they are attached to non-diffusible molecules Na+/K+ pumps are electrogenic- pumping 3 Na+ out for every 2K+ pumped in Usually -70 mV - polarized

Diverging circuit

: one presynaptic neuron influences several postsynaptic neurons/ muscle fibers/gland cells the same time Diverging circuit: presynaptic neuron causes stimulation of increasing numbers of cells along the circuit

Parallel after-discharge

: single presynaptic cell stimulates a group of neurons, each of which synapses with a common postsynaptic cell

Saltatory conduction

: special mode of action potential propagates along myelinated axons, occur bc of uneven distribution of voltage gated channels, these voltage gated channels in the nodes of Ranvier Myelin sheath speeds up action potential Voltage changes at Nodes of Ranvier More energy efficient

Continuous Conduction

: step-by step depolarization and repolarization of each adjacent segment of the plasma membrane- propagates only a relatively short distance Occurs on unmyelinated axons in muscle fiber

Carbon monoxide

:not produced in advance like NO, excitatory neurotransmitter produced in the brain and in response to some neuromuscular and neuro glandular functions: dilation of blood vessels, memory, olfaction

Neural circuits

A neural circuit is a functional group of neurons that process specific types of formation

Reflexes and reflex arcs

A reflex is a fast, predictable, automatic response to changes in the environment Reflexes help maintain homeostasis Spinal cord serves as the integrating center for spinal reflexes Integration takes place in the gray matter of the spinal cord

Signal Transmission in synapses - gap junction

A synapse is the junction between neurons or between a neuron and an effector Gap junctions connect cells and allow the transfer of information to synchronize the activity of a group of cells Faster communication- bc no synapse, synchronization- large number of of neurons or muscle fibers can produce action potentials in unison Found in brain, between cardiac muscle/smooth muscle fibers; intercalated discs- example of electrical synapse

Action potential: stimulus strength

Action potentials can only occur if the membrane potential reaches threshold: -55mV Subthreshold stimulus: weak depolarization that cannot bring the membrane potential to threshold Threshold stimulus: just strong enough to depolarize the membrane to threshold Suprathreshold stimulus: stimulus that is strong enough to depolarize the membrane above threshold

Autonomic nervous system

Autonomic sensory receptors and autonomic sensory neurons are sent to CNS Autonomic motor neurons (involuntary- can't control): sympathetic and parasympathetic divisions - sent to smooth muscle, cardiac muscle and glands

Synapse between neurons

Axoaxonic: attach axon to axon Axodendritic: attach axon to dendrite Axosomatic: attach axon to cell body

Factors that Affect propagation speed

Axon diameter: thicker diameter (wider) faster than narrow axons- faster in general myelinated than unmyelinated Amount of Myelination- faster in general myelinated than unmyelinated Temperature: axons propagate action potential at lower speeds when cooled

Axillary

C5-C6; deltoid and teres minor muscles; skin over deltoid and superior posterior aspect of arm

Musculocutaneous

C5-C7: coracobrachialis, biceps brachii, and brachialis muscles

Median

C5-T1 flexors of forearm, except flexor carpi ulnaris; ulnar half of flexor digitorum profundus, and some muscles of hand (lateral palm); skin of lateral two-thirds of palm of hand and fingers

Radial

C5-T1; triceps brachii, anconeus, and extensor muscles of forearm; skin of posterior arm and forearm, lateral two-thirds of dorsum of hand, and fingers over proximal and middle phalange

Ulnar

C8-T1: flexor carpi ulnaris, ulnar half of flexor digitorum profundus, and most muscles of hand; skin of medial side of hand, little finger, and medial half of ring finger

Layout of Nervous System

CNS: Brain and Spinal cord PNS: cranial nerves, spinal nerves, ganglia, enteric plexuses in small intestine, and sensory receptors in si

Internal anatomy of spinal cord

Central canal: extends whole spinal cord, contains cerebrospinal fluid Gray matter of spinal cord: clusters of neuronal cell bodies called nuclei Sensory nuclei receive input from receptor via sensory neurons and motor nuclei provide output to effectors Cell bodies of sensory neurons are located in the posterior root ganglion of a spinal nerve Lateral gray horns contain autonomic motor nuclei: clusters of cell bodies of autonomic motor neurons which regulate activity of cardiac muscle, smooth muscle, glands White matter: each column contains distinct bundle of axons

Dermatomes

Certain segments of the skin are supplied by spinal nerves that carry somatic sensory nerve impulses into the spinal cord and brain Little loss of sensation may result if only one of the nerves supplying the dermatome is damaged

Spinal plexuses with representative spinal nerves

Cervical plexus, brachial plexus, lumbar plexus, sacral plexus, coccygeal plexus

Meninges

Composed of three layers Dura mater: outer layer Arachnoid mater: spider web like projections Pia mater: adheres directly to spinal cord Spaces of each are also important Epidural (interstitial fluid), subarachnoid space, cerebrospinal fluid)

Homeostatic imbalances

Damage that results from traumatic injuries depends on Degree of spinal cord section or Degree of compression of the segments involved Person has loss of dermatome functions

Graded potential: summation

Dendrites to cell bodies Graded depolarizing potentials can add together and become larger in amplitude Action potentials don't summate

Removal of neurotransmitter

Diffusion, enzymatic degradation, uptake of cells

Connective Tissue covering spinal nerves

Each individual axon, unmyelinated and myelinated are covered in endoneurium the innermost layer Mesh of collagen fibers, fibroblasts, macrophages Group of axons with endourium held together by bundles called fascicles Each fascicles wrapped in perineurium Outermost layer is epineurium Fuses with dura mater

Neurons

Electrically excitable Cellular structures

Enteric Nervous system

Enteric sensory receptors and enteric sensory neurons in gastrointestinal tract and enteric plexuses to CNS Sends enteric motor neurons (involuntary) in enteric plexuses to smooth muscle, glands, and endocrine cells of GI tract

Electrical Signals in Neurons

Excitable cells communicate with each other via action potentials or graded potentials Action potentials (AP) allow communication over short and long distances whereas graded potential (GP) allow communication over short distances only Production of an AP or GP depends upon the existence of a resting membrane potential and the existence of certain ion channels Graded potentials- brings neuron closer to generating an axon potential

Postsynaptic potentials

Excitatory postsynaptic potentials: depolarizing postsynaptic potential Inhibitory postsynaptic potentials: hyperpolarizing potential A postsynaptic neuron can receive many signals at once

Comparison of Graded and Axon potential

Graded potential dies out due to opening and closing of ligand gated channels depolarizing and hyperpolarizing Action potentials- "all or nothing", must hit threshold, always depolarizatio

Gray matter

Gray matter in horns of spinal cord and outer cerebral cortex of brain Unmyelinated axons, cell bodies

Spinal Cord Physiology

How does information travel in the spinal cord? White matter tracts conduct nerve impulses to and from the brain Gray matter receives and integrates incoming and outgoing information to perform spinal reflexes

Neurogenesis in the CNS

In the CNS, there is little or no repair due to: Inhibitory influences from neuroglia, particularly oligodendrocytes Absence of growth-stimulating cues that were present during fetal development Rapid formation of scar tissue

Damage and repair in the PNS

In the PNS repair is possible if the cell body is intact, schwann cells are functional and scar tissue formation does not occur too rapidly Steps involved in the repair processes are Chromatolysis: Wallerian degeneration: Formation of a regeneration tube:

Reflex Arc vocab

Ipsilateral: same side Contralateral: different side Monosynaptic: one synapse Polysynaptic: multiple synapses Reciprocal innervation:components of a neural circuit simultaneously cause contraction of one muscle and relaxation of its antagonists Intersegmental: between segments

Action potentials

Is a sequence of rapidly occurring events that leads to a reversal of the membrane potential (depolarization) followed by a restoration to the resting state (repolarization) Occurs on axon Graded potential depolarizes, makes it easier for neuron to generate action potential Hyperpolarizing action potential- makes it harder for neurons to generate action potential Sodium rushes into neuron at peak of action potential, K+ rushes out "All or none"- must reach -55 mV or you don't Depolarizing graded potential: makes cell membrane more positive Na+/K+ pump: restores action potential to action potential

Obturator

L2-L4: adductor muscles of hip joint; skin over medial aspect of thigh

Femoral

L2-L4: largest nerve arising from lumbar plexus; distributed to flexor muscles of hip joint and extensor muscles of knee joint, skin over anterior and medial aspect of thigh and medial side of leg and foot

Sciatic

L4-S4: two nerves: tibial and common fibular- bound together by common sheath of CT; spit into two divisions usually at the knee, sciatic nerve descends through thigh, it sends branches to hamstring muscles and adductor magnus

Leak Channels

Leak channels alternate between open and closed K+ channels are more numerous than Na+ channels Channels randomly open and close Found in all cells, including dendrites, cell bodies

Signal transmission at a chemical synapse

Ligand gated channels receives neurotransmitter- stimulated hyperpolarized/depolarized impulse

Crossed-Extensor Reflex

Maintains balance Polysynaptic, contralateral

Factors contributing to resting membrane potential

More K+ than Na+ pumps Anions 3 Na out for 2 K in

Flexor (withdrawal) reflex

Moves a limb to avoid injury or pain Ipsilateral, polysynaptic: multiple neurons, runs to different segments of spinal cord Reciprocal innervation; Intersegmental reflex: several segments of the spinal cord interneurons are activated

Structural classification of neurons

Multipolar Neuron: has dendrites surrounding cell body Bipolar neuron: dendrites travel down before reaching the cell body in middle of the axon Unipolar neuron: cell body branched off of a central process- most are sensory receptors that sense pain, touch, pressure

Structure of neurotransmitter receptors

Neurotransmitters at chemical synapses cause either an excitatory or inhibitory graded potential Neurotransmitter receptors have two structures

Parts of Neurons

Nissl bodies: clustered ER used to regenerate damaged axons in the PNS Neurofibrils and Microtubule: provide support and movement for cell body and axon Dendrites: receive input Axon: propagates nerve impulse- contains axon hillock, , initial segment, trigger zone

Neuroglia

Not electrically excitable Make up about half the volume of the nervous system Can multiply and divide 6 kinds total (4 in CNS, 2 in PNS) Not just neurons make up nervous system

Neuroglia in CNS

Nucleus processes: making multiple myelo dendrites Astrocytes: help maintain blood/brain barrier Microglial- only found in CNS Microglial cells- immune response Oligodendrocyte - myelinates axons in the CNS Cerebrospinal fluid: fluid that protects spinal cord

Action potential: status of Na+ and K+ voltage gated channels

Only respond to -55mV threshold in action potential Closed in resting state 1. Resting state: voltage gated Na+ and K+ are closed positive outside, negative inside 2. Depolarizing phase: membrane potential reaches threshold, Na+ channels open, Na+ moves in and builds positive charge forms along inside surface of membrane and the membrane becomes depolarized 3. Repolarizing phase begins: Na+ channels close and K+ channels open, membrane starts to repolarize 4: Repolarization phase continues: K+ continue to flow out

Regeneration and Repair of Nervous Tissue

Plasticity, regeneration

Summation of Postsynaptic Potentials

Presynaptic neurons release excitatory neurotransmitters that generate excitatory postsynaptic potential

Functions of the spinal cord

Process reflexes Integrate excitatory postsynaptic potentials (EPSP) and and inhibitory postsynaptic potentials (IPSPs) Integrating center (excitatory/inhibitory) Conduct sensory impulses to the brain and motor impulses to effectors

Examples of dendritic branching

Purkinje cell - large amounts of branched dendrites and axon terminals Pyramidal cell- branching of dendrites around axons more spaced out

Stretch Reflex

Reflex arc is monosynaptic Only one synapse between sensory neuron Leg extends, responds by contracting Exhibits reciprocal innervation

Clinical connection

Reflexes are often used for diagnosing disorders of the nervous system and locating injured tissue If a reflex is absent or abnormal, the damage may be somewhere along a particular conduction pathway Patellar reflex, achilles reflex, babinski sign, abdominal reflex

Prudendal

S2-S4: muscles of perineum; skin of penis and scrotum in male, clitoris, labia majora, labia minora, and vagina in female

Neuroglia of PNS

Schwann and satellite cells seen in peripheral

Branches of spinal nerve

Shortly after passing through its intervertebral foramen of a spinal nerve divides into several branches known as rami

Graded potential

Small deviations in resting membrane potential A graded potential occurs in response to the opening of a mechanically-gated or ligand-gated ion channel Hyperpolarizing graded potential: when response makes the membrane more polarized Harder to generate nervous impulse Depolarizing graded potential: when response makes the membrane less polarized Easier to generate nervous impulse

Organization of the Nervous System

Somatic Nervous System, Autonomic Nervous system, enteric nervos system

Spinal Nerves

Spinal nerves connect the CNS to sensory receptors, muscles, and glands and are a part of the PNS 31 pairs of spinal nerves Anterior and posterior roots attach a spinal nerve to a segment of the spinal cord

Neuropeptides

Substance P: perception of pain Enkephalins and endorphins: stimulate release of pain by exercise, reduce release of substance P Dynorphins: related to controlling pain and registering emotions Hypothalamic releasing and inhibiting hormones: regulate release of hormones by anterior pituitary Angiotensin II: stimulate thirst; may regulate blood pressure in brain- increase rate of water and salt reabsorption in kidneys Cholecystokinin (CCK)- "stop eating" signal, regulates pancreatic enzyme during digestion, smooth muscle contraction in gastrointestinal tract

gluteals

Superior gluteal L4-L5 and S1: gluteus minimus, gluteus medius, and tensor fasciae latae muscles Inferior gluteal L5-S2: gluteus maximus muscle

Graded potential: stimulus strength

The amplitude of a graded potential depends on the stimulus strength Strength is determined by how many ions are entering/leaving cells Different strengths of grated potential cause Greater the stimulus strength the larger the amplitude of the graded potential

Sensory and Motor processing

The internal anatomy of the spinal cord allows sensory and motor information to be processed in an organized way Posterior: sensory info Anterior: motor neuron

Myelination of Neurons

The myelin sheath is produced by Schwann cells (PNS) or oligodendrocytes (CNS) and surrounds the axons of many neurons Prevents axon from being damaged PNS axons can be repaired b/c of neurolemma

External anatomy of spinal cord

The spinal cord begins as an extension of the medulla oblongata at the level of the foramen magnum and it terminates at the level of L2

Protection of the spinal cord

The spinal cord is protected by Bone (vertebrae) Connective tissue (meninges) Superficial to deep: dura mater, epidural space, arachnoid mater, pia mater Fluid (cerebrospinal fluid)- found in subarachnoid space

Graded Potentials and Action potentials

Tract- bundle of neuron fibers within CNS Ganglion- neuron cell bodies outside the CNS Nucleus- neuron cell bodies within the CNS

White matter

White matter of spinal cord- outside and lateral columns and inner part of brains Myelinated axons

Integrative

analyze incoming sensory information, store some aspects, and make decisions regarding appropriate behaviors

Lumbar plexus

anterolateral abdominal wall; external genitals; part of lower; limbs, femoral, obturator

sensory tract

ascending

Sacral plexus

buttocks, perineum, lower limbs; gluteals, sciatic, prudendal

sensory/afferent neuron function

carried into CNS through cranial or spinal nerve

inotropic receptors

contains neurotransmitter binding site and an ion channel, same protein as ion channel

Tendon reflex

controls muscle tension by causing muscle relaxation Detects tension being built up Polysynaptic: two synapses Ipsilateral: same sides Reciprocal innervation: agonist relaxes, antagonists contracts

Posterior column

convey nerve impulses for discriminative touch, light pressure, vibration, and conscious proprioception (position and movement of muscles, tendons, joints); Sensory systems keep the CNS informed of the changes in the external and internal environment

Spinothalamic tract

convey nerve impulses for sensing pain, warmth, coolness, itching, tickling

Wallerian degeneration

degeneration of the distal portion of the axon and myelin sheath

motor tract

descending

ATP and other purines

excitatory neurotransmitter in both the CNS and PNS ATP, ADP, AMP (monophosphate

Nitric oxide

excitatory neurotransmitter secreted in the brain, spinal cord adrenal glands, and nerves to the penis; not synthesized in advance and packaged into synaptic vesicles, formed on demand and acts immediately

Summation

if several presynaptic end bulbs release their neurotransmitter at about the same time, the combined effect may generate a nerve impulse due to summation

Enzymatic degradation

inactivated through enzymatic degradation; ex: ACh is broken down by AC

Temporal summation

is summation of postsynaptic potential in response to stimuli that occur at the same location in the membrane of the postsynaptic cell but different times

Neurotransmitters

larger molecules: like substance P

Inter/association neurons

located within the CNS between sensory and motor- integrate incoming sensory information; most are multipolar

Uptake of cells

many neurotransmitters are actively transported back into the neuron that released them released by reuptake

Amino Acids

neurotransmitters in the CNS Ex: glutamate and aspartate- binding opens cation channels Gamma-aminobutyric acid (GABA) inhibitory neurotransmitters, open Cl- channels

Chemical synapse

one-way transfer of information from a presynaptic neuron to a postsynaptic neuron Separated by synaptic cleft within interstitial fluid Communication across synapse to postsynaptic neuron creates postsynaptic potential (graded) This takes longer- causes synaptic delay 1. Nerve arrives at synaptic end bulb 2. Depolarizing phase of nerve opens voltage gated Ca2+ channels, Ca flows in 3. Increase in [Ca] triggers exocytosis of synaptic vesicles- neurotransmitters cross synaptic cleft 4. Neurotransmitter diffuses across synapse and bind to neurotransmitter receptor in postsynaptic neuron's plasma membrane 5. Binding of neurotransmitters molecules to their receptors on ligand gated channels opens the channels and allows particular ion to flow across 6. Postsynaptic potential changes depending on open ion channels; opening Cl- or K+ causes hyperpolarization 7. When depolarization postsynaptic potential reaches threshold, it triggers an action potential in axon Synapse between neuron and effort- smooth muscle, skeletal muscle, glands receive messages

Converging

postsynaptic neuron receives nerve impulses from several different sources- input from several pathways that originate in different brain regions

Simple series

presynaptic neuron stimulates one single postsynaptic neuron

Acetylcholine

released by many PNS neurons and causes the opening of cation channels

Motor neuron

respond to stimuli

Ligand-gated channels

s respond to chemical stimuli (ligand binds to receptor) When ligand binds: sodium gated channels change shape Dendrites of some sensory neurons such as pain receptors

Voltage gated channels

s respond to direct changes in membrane potential Found in neurons and excitable tissues Axons of all types of neurons

Mechanically-gated channels

s respond to mechanical vibration or pressure stimuli- touch, pressure, tissue stretching Dendrites of some sensory neurons such as touch receptors, pressure, pa

Formationof a regeneration tube

schwann cells on either side of the injured site multiply by mitosis, grow toward each other and may form regeneration tube which guides growth of a new axon from the proximal area across the injured area to distal area

Somatic nervous system

sends information to CNS via somatic and special sensory receptors and somatic sensory neurons Receives info by somatic motor neurons (voluntary- can control) which then sends to skeletal muscles

Sensory neuron

sense changes through sensory receptor

Brachial

shoulders and upper limbs, musculocutaneous, axillary, median, radial, ulnar

Cervical

skin and muscles of head, neck, superior part of shoulders and chest, phrenic nerves of cervical plexus supply motor fibers to diaphragm

Coccygeal Plexus

small area of skin in coccygeal region, anterior rami of spinal nerves S4-S5 and the coccygeal nerves

Diffusion

some neurotransmitter molecules diffuse away from synaptic cleft, once molecule is out of reach of its receptors it can no longer exert an effect

two main routes on each side of spinal cord

spinothalamic tract, posterior column

Spatial summation

summation of postsynaptic potentials in response to stimuli that occur at different location in membrane of postsynaptic cell

Chromatolysis

the Nissl bodies break up into fine granular masses

Plasticity

the capability to change based on experience Sprouting of new dendrites, synthesis of new proteins, changes in synaptic contacts with other neurons

Regeneration

the capability to replicate or repair Damage to dendrites and myelinated axons may be repaired if the cell body remains intact and if the schwann cells that produce myelination remain active

motor./efferent neurons

to carry away from CNS to PNS through cranial or spinal nerves