AAMC Study Guide. Content Category 3A: Structure and functions of the nervous and endocrine systems and ways in which these systems coordinate the organ systems

Reflexes - Role of spinal cord and supraspinal circuits

- Spinal cord provides the synapse (or synapses if it's polysynaptic) for the reflex arc. - Even though the reflex arc bypasses the brain, the brain is still aware of it happening. efferent control - Brain can override spinal reflexes (eg. you don't jerk away from getting a vaccine shot)

Resting potential: electrochemical gradient

- The sodium-potassium pump pulls potassium ions in and moves sodium ions out of the cell. - Because potassium is positively charged and the inside of the cell is negatively charged, the electrical gradient tends to pull potassium in, not out. - When a membrane is at rest, sodium ions are more concentrated outside of the neuron; potassium ions are more concentrated inside. - - Concentration gradients move potassium ions out of the cell. resting potential = Neuron membrane potential is slightly negative Graded potentials = produce either depolarization or hyperpolarization, depending on the stimulus. Action potentials = are characterized by rapid depolarization. - Refractory periods (both relative and absolute) are times when a membrane is resistant to starting another action potential.

Excitatory and inhibitory nerve fibers: summation, frequency of firing

1) Excitatory nerve fibers (EPSP) - The binding of Ach to Post syn membrane receptor elicits and excitatory response that generates an AP - Referred to as Excitatory Post Syn Potentials Suppose Neuron A (with 6APs) synapses with Neuron C - If the connection is excitatory, - The same # of AP that pass down the axon of neuron A will also pass down axon of Neuron C - There will be an increase in the permeability of post syn membrane to Na+ (EPSP) - and neuron C will depolarize (continue AP) summation, frequency of firing - If we integrated the APs that Neuron C receives from Neuron A - we find that neuron C generates 6 APs --> (6→6) 2) Inhibitory nerve fibers (IPSP) - There can also Inhibutory Post Syn Potentials Suppose Neuron B (inhibitory with 4APs) also synapses with Neuron C - There will be an increase in the permeability of post syn membrane to K+ and Cl- (IPSP) - and neuron C will hyperpolarize (stop AP) summation, frequency of firing - If we integrated the APs that Neuron C receives from both A and B - we find that neuron C only generates 2 APs --> (6-4 = 2) - neuron B decreased the excitability of neuron C to the stimulation it received from neuron A

Cell body: site of nucleus, organelles Dendrites: branched extensions of cell body

A Nerve Cell is Composed of; 1. Dendrites - receives and transmits electrical info to cell body 2. Cell body - integrates/process info 3. Axon - takes info away from cell body CELL BODY aka SOMA - site of nucleus, organelles - just like any other cell DENDRITES - branched extensions of cell body

Glial cells, neuroglia https://www.khanacademy.org/test-prep/mcat/organ-systems/neural-cells/v/astrocytes

Astrocytes

Synapse: site of impulse propagation between cells

At end of axon = synapse bulb - Can *synapse* on another axon of a different neuron, dendrite, cell body eg muscle - (impinge, encroach on, intrude on, infringe on, invade, trespass on, interfere with) Synaptic Cleft - Space between synapse junction Pre-synaptic membrane - Plasma membrane at end of axon/synapse bulb Post-synaptic membrane - Plasma membrance that the synapse is being made to

Axon: structure and function

Consists of; - Myelin sheath - Schwann cells - Node of Ranvier

Reflexes - Feedback loop

Feedback loop = 1. positive feedback (reinforce initial event), 2. negative feedback (counteracts initial event), or 3. reflex arc (usually a type of negative feedback). positive feedback = uterine contraction lead to oxytocin release, which causes more uterine contraction. positive feedback = blood clotting platelets activated at wound site attract more platelet activation and clumping. negative feedback = drop in blood pressure causes ADH release, which increases it. Conversely increase in blood pressure causes a drop in ADH. Reflex arc = withdrawal from a painful stimulus = negative feedback. Reflex arc = knee jerk = tapping the knee tendon causes sudden stretching of the muscle, which lead to contraction of that muscle that creates the knee jerk = negative feedback.

Synaptic activity: transmitter molecules

Let's consider a Neuromuscular Junction - This is the synapse between the synapse bulb of an axon and a muscle fiber - Within the synapse bulb of this junction are hundreds of thousands of synaptic vesicles - These synaptic vesicles contain the neurotransmitter --> Acetylcholine (Ach) As the AP reaches the synapse bulb - It triggers the opening of --> Calcium (Ca2+) channels from extracellular fluid to the cytosol - An influx of Ca2+ channels into the terminal region - causes the synaptic vesicles to fuse with the presynaptic membrane - and release the neurotransmitter (Ach) into the synaptic cleft via exocytosis - The released Ach diffuses through the synaptic cleft - and binds to specific post synaptic membrane receptors - This binding conformationally changes the receptor - into a channel (ionophore) that is large enough to allow cations such as Na+ through. - As Na+ enters the postsynaptic membrane - Muscle fiber begins to depolarize and AP is eventually generated. Acetylcholine (Ach) - Is synthesized in the cytosol of the neuron - from Acetyl CoA Calcium Channels - comes from the extracellular fluid to the cytosol to trigger the release of Ach OTHER - Glutamate - Epinephrine - norepinephrine - dopamine - seratonin - drugs

Major Functions

Major Functions - High level control and integration of body systems - Adaptive capability to external influences sensory input sensory = afferent nerve impulses conveyed to the CNS. motor output motor = efferent nerve impulses from the CNS to effector organs. - Basic functions are associated with the senses, movement, and automatic function. - Higher functions are associated with cognition, emotion, or consciousness. Feeling fear is a component of emotion, a higher function associated with the experience of life. Language acquisition is a form of learning associated with cognition. An experience of pain would be associated with basic sensory function, but remembering that pain is associated with higher function. Sweat is a form of body temperature regulation, which is performed automatically and does not require conscious involvement. It is a basic function.

Myelin sheath, Schwann cells, insulation of axon

Myelinated Nerves - Have ability to greatly increase rate of APs - Composed of protein and phospholipids Glial Cells - A specialized type of cell that attaches itself to a section of the unmyelinated axon - and begins to rotate itself around the axon a number of times *Myelin Sheath* - This causes a myelin sheath to be deposited on the axon Node of Ranvier - The areas where there is no Myelin Sheath deposit Olidodendrocytes - The glial cells in the CNS *Schwann Cell* - The glial cells in the PNS - Makes myelin sheath in the peripheral nervous system by wrapping around the axon. *Insulation of axon* - The myelin that is deposited on the axon acts as an electric insulator - and prevents the transfer of ions across the plasma membrane of the axon - The only region where ions can pass across the plasma membrane is the Node of Ranvier SUMMARY Nerve fibers can be grouped into 2 1. Myelinated Nerves - Transmit motor impulses quickly - greatly increases rate at which info (AP) is conducted 2. Unmyelinated Nerves - Transmit sensory impulses slowly

Nodes of Ranvier: propagation of nerve impulse along axon

NODE OF RANVIER - propagation of nerve impulse along axon - The only region where ions can pass across the plasma membrane is the Node of Ranvier NOR contain high amount of Na+ channels - As an AP is generated - There is a flow of current through the axoplasm of the axon (cytoplasm) and the extracellular fluid from node to node - The plasma membrane at each node is depolarized enough to generate an AP - The nerve impulse transmission seem to "jump" from node to node along the axon --> hence referred to as saltatory conduction

*Nerve Cell (BIO)*

Nervous system = Nerve cells + other supporting cells Nerve Cells = Neurons - Basic unit of nervous system - receives and processes electrical info in the form of (Stimulus) - then transmits it down the axon in the form of (Nerve impulse) --> called an Action Potential (AP) - When AP reaches end of axon/synaptic bulb - A chemical substances is released --> called Neurotransmitter - Neurotransmitter diffuses across synaptic cleft - (space between pre and postsynaptic membrane, also known as synaptic junction) - Here it induces an identical AP in another neuron, muscle cell, or gland cell (stimulus → nerve Impulse → AP1(pre) → Neurotransmitter → AP2(post)...)

Sensor and effector neurons

PNS has 2 types of Neurons; 1. Afferent/SENSOR Neurons - Carries information away from the skin into the spinal cord and brain 2. EFFERENT/motor + ANS Neurons - Carries information from the spinal cord and brain to the tissues - Motor neuron = Skeletal muscles - ANS/Viseral neurons = Cardiac, smooth muscles and glands cells

Sympathetic and parasympathetic nervous systems: antagonistic control https://www.khanacademy.org/test-prep/mcat/organ-systems/biological-basis-of-behavior-the-nervous-system/v/autonomic-nervous-system

Peripheral Nervous System (PNS) ↓ EFFERENT/motor Neurons 1. Motor/Somatic Nervous System = Voluntary = Controls skeletal muscles. 2. Autonomic Nervous System = Involuntary = (efferent neurons, cardiac & smooth muscles gland cells) - Affects visceral organs. Autonomic Nervous System (ANS) - Nerve fibers from ANS leave the spinal cord to innervate various glands, and muscles - ANS has 2 nervous systems 1. Sympathetic nervous systems (scared) Location - Nerve fibers leave from midbrain, medulla and the sacral portion of spinal cord - Sympathetic nerves have a short axon to the synapse of another neuron, then a long axon to the target neuron. Function = Rest and Digest - Pupils dilate (wild open) - increased heart rate - increased blood pressure - decreased rate of digestion (due to ↓ blood flow to intestines) - increased sweat from sweat glands - Break down glycogen to release glucose into blood. 2. Parasympathetic nervous systems (peace) Location - Nerve fibers leave from thoracic and lumbar regions of spinal cord - Parasympathetic nerves have long axons to the synapse of another neuron, then a short axon to the target neuron. Function = Fight or flight - Pupils constrict/contract - lower heart rate - lower blood pressure - Increase rate of digestion (due to ↑ blood flow to intestines) - Increased saliva from salivary gland - Synthesizes glycogen for storage from glucose. In general; - conserves energy - restores bodily functions

Reflexes - Reflex arc

Reflex arc = stimulation of the nerve that cause contraction - If you are tapped on the knee with a rubber hammer - Your lower leg will extend outward - This is because the impulses from the sensory neuron (away) travel along an axon to the spinal cord and synapses with 2 neurons 1st synapse = motor neuron - immediately leaves spinal cord to the quadriceps/extensor muscles in front of leg --> causing a contraction and the leg straightens/extends at knee joint - synapse is called the monosynaptic reflex arc 2nd synapse = interneuron (inhibitory) - immediately leaves spinal cord to the bicep/flexor (hamstring) muscles in back of leg --> causing a contraction and the leg bends at knee joint - synapse is called the polysynaptic reflex arc Reflex arc = receptor → sensory neuron → integration center → motor neuron → effector receptor = site of stimulus sensory neuron = carries impulse from receptor to integration center integration center = connects sensory to motor neuron via synapse inside the CNS monosynaptic = no interneuron, direct synapse of sensory to motor. polysynaptic = interneuron(s) present. motor neuron = carries impulse toward effector. effector = site of response to the stimulus

Organization of vertebrate nervous system https://www.khanacademy.org/test-prep/mcat/organ-systems/biological-basis-of-behavior-the-nervous-system/v/structure-of-the-nervous-system

The Nervous System ↓ 2. Central Nervous System (CNS = Brain + Spinal Cord - connected by The Brain stem - consists of midbrain, pons, medulla 2. Peripheral Nervous System (PNS) = Nerves that extend from the spinal cord The 3 basic anatomical division of brain 1. Forebrain (prosencephalon) - cerebrum 2. Midbrain (mesencephalon) 3. Hindbrain (rhombencephalon) - Pon - Medulla - Cerebellum NOTE: Cerebellum = coordinates movement. Cerebral Cortex = Processing occur here eg Sensation of pain - Cerebrum is the largest and the most prominent part of the brain, whereas the - Cerebral cortex is the outer layer of the cerebrum. - Cerebral cortex is actually a part of the cerebrum. - The cerebrum has both gray and white matter, whereas the gray matter is considered to be the cerebral cortex. - The occipital lobe is involved with vision. - The temporal lobe is involved with memory, emotion, hearing, and language - The frontal lobe is involved with decision making, problem solving, and planning. - The parietal lobe is involved with sensation and perception.

Action potential - Threshold, all-or-none - Sodium/potassium pump

The all-or-none rule states that the size, amplitude, and velocity action potentials are independent of the intensity of the stimulus that initiated it, whereas graded potentials are proportional to the intensity or magnitude of the stimulus that initiated it. Graded potentials are decremental, meaning that their amplitude diminishes as they travel away from the original site; action potentials do not diminish in amplitude. Graded potentials can be hyperpolarizing or depolarizing, depending on the stimulus. Action potentials are always depolarizing.

OVERVIEW - the structure of nervous and endocrine systems - function of nervous and endocrine systems - basic aspects of nervous and endocrine systems - their integration. - The structure and function of nerve cells

The nervous & endocrine systems work together to - detect external and internal signals, - transmit and integrate information, and - maintain homeostasis. They do all of this by producing appropriate responses to internal & external cues and stressors. The integration of these systems both with one another & with the other organ systems, ultimately results in the successful and adaptive behaviors that allow for the propagation of the species. Animals have evolved a nervous system that senses and processes internal and external information that is used to facilitate and enhance survival, growth, and reproduction. The nervous system interfaces with sensory and internal body systems to coordinate physiological and behavioral responses ranging from simple movements and small metabolic changes to long-distance migrations and social interactions. The physiological processes for nerve signal generation and propagation involve specialized membranes with associated proteins that respond to ligands and/or electrical field changes, signaling molecules and, by extension, the establishment and replenishment of ionic electrochemical gradients requiring ATP. The endocrine system of animals has evolved to produce chemical signals that function internally to - regulate stress responses, - reproduction, - development, - energy metabolism, - growth, and - various individual and interactive behaviors. The integrated contributions of the nervous and endocrine systems to bodily functions are exemplified by the process whereby the signaling of neurons regulates hormone release, and by the targeting of membrane or nuclear receptors on neurons by circulating hormones.

*Electrochemistry (GC)* - Concentration cell: direction of electron flow, Nernst equation

direction of electron flow, Nernst equation