Chapter 12

Grey matter

(gray because it lacks myelin) of the brain and spinal cord is formed from neuronal cell bodies and dendrites.

The Somatic nervous system consists of

1. sensory neurons that convey information from somatic receptors in the head, body wall, and limbs and from receptors for special senses (hearing, seeing, etc) 2. Motor neurons that conduct impulses from the CNS to skeletal muscles only.

CNS consists of

brain and spinal cord

most neurons have 3 parts

cell body (soma), dendrites and an axon

Axon hillock

Portion of the neuron that connects the cell body, soma, to the axon. The impulses the neuron receives from all the dendrites are summed up at the axon hillock to determine whether an action potential will be initiated.

CNS

Processes many different kinds of incoming sensory information. It is also the source of thoughts, emotions, and memories. Most signals that stimulate muscles to contract and glands to secrete originate here.

Enteric plexuses

extensive networks of neurons located in the walls of rogans of the gastrointestinal tract.

Synaptic cleft

Small gap between the presynaptic and postsynaptic membranes of a synapse.

Postsynaptic neuron

The neuron receiving the information

Initial segment

The portion of the axon between the axon hillock and the point at which myelination begins; the site where various excitatory and inhibitory stimuli are summed, resulting in the decision to propagate or not to propagate an action potential

Myelination

The process of forming a myelin sheath which insulates and increases nerve impulse speed. It is formed by Oligodendrocytes in the CNS and by Schwann cells in the PNS.

Synapse

The site of communication between two neurons or between a neuron and another effector cell is called a synapse.

Synaptic end bulbs

The tips of some axon terminals swell into these bulb-shaped structures that contain synaptic vesicles

Bipolar neurons

have one main dendrite and one axon. They are used to convey special senses of sight, smell, hearing and balance. the TRUNk is the dendrite not the branches. Found in retina of eye, the inner ear and the smelling area of the brain

Oligodendrocytes

i. Few branches (at least compared to Astrocytes and Microglia). ii. These cells line up along thicker neuron fibers in the CNS and wrap their extensions around nerve fibers forming the myelin sheath to insulate the neurons from each other. 3. Provides framework? Produce myelin like Schwann cells

Schwann cells

i. Forms the myelin sheath around large nerve fibers in the PNS. ii. Can also act as phagocytic cells that engulf damaged or dying nerve cells and are important in directing the process of regeneration. iii. The myelin sheath forms by the Schwann cells wrapping around and around the axon. 4.Participates in repair process after injury Gaps between the Schwann cells are called the Nodes of Ranvier.

Ependymal cells

i. Line the central cavities of brain and spinal cord, creating a barrier between the CNS cavities and the tissues surrounding the cavities. ii. Ependymal cells assist in producing, monitoring, and circulating cerebrospinal fluid, CSF. iii. They use their cilia to circulate the CSF within the cavities of the CNS.

Microglia

i. Ovoid cells with highly branched processes ii. These act as macrophages that engulf microbes and dead neural cells as well as remove cellular debris, waste products, and pathogens. (Phagocytosis)

Satellite cells

i. These surround the nerve cell body. ii. May aid in controlling chemical environment about the neuron much like the astrocytes of the CNS.

PNS consists of

all nervous tissue outside the CNS.

Leaked channels

also gated but are not active and open and close randomly

Flow of ions like

an electrical current going between two batteries and a piece of wire

membrane potential

an electrical potential difference (voltage) across the membrane. like voltage stored in a battery.

An action potential (nerve impulse)

an electrical signal that propagates along the surface of the membrane of a neuron.

Interneurons or association neurons

mainly located within the CNS between sensory and motor neurons. They Integrate (process) incoming sensory information from the sensory neurons and then elicit a motor response by activating the appropriate motor neurons. Most are multipolar

White matter

of the brain and spinal cord is formed from aggregations of myelinated axons from many neurons. The lipid part of myelin imparts the white appearance.

Action potentials cannot

propagate across a synaptic cleft. Instead, neurotransmitter are used to communicate at the synapse, and re-establish the AP in the postsynaptic cell.

Axon

propagates nerve impulses toward another neuron, a muscle fiber

Dendrites

receiving or input potions of a neuron. They are short, highly branched structures that conduct impulses toward the cell body.

Ligand-gated channels

respond to a neurotransmitter and are mainly concentrated at the synapse.

Voltage-gated channel

respond to changes in the transmembrane electrical potential and are mainly located along the neuronal axon.

Mechanically-gated channels

respond to mechanical deformation (applying pressure to a receptor.)

Multipolar neurons

several dendrites and only one axon and are located throughout the brain and spinal cord. (vast majority of neurons)

Graded potentials

short-distance communication only

Ganglia

small masses of nervous tissue, consisting primarily of neuron cell bodies, that are located outside of the brain and spinal cord.

Neuroglia

smaller than neurons but greatly outnumber them. They are the "glue" that supports and maintains the neuronal networks.

PNS is divided into

somatic nervous system, autonomic nervous system, and an enteric nervous system.

The motor part of the ANS consists of two branches

sympathetic and parasympathetic

Action potentials

Allow communication over long distances within the body.

Neuroglia

Also known as glia, are cells that support and take care of the neurons.

Neuroglia in CNS

Astrocytes, oligodendrocytes, microglia, and ependymal cells

nerves, ganglia, enteric plexuses, and sensory receptors.

Components of PNS

Presynaptic neuron

Conducts impulses toward the synapse

Sensory neurons. What they convey and what most are

Convey action potentials into the CNS through cranial or spinal nerves. Most are unipolar

Sensory function (afferent)

DETECT internal stimuli such as an increase in blood pressure and external stimuli. This sensory information is then carried into the brain and spinal cord through cranial and spinal nerves

Motor function (effectors)

Eliciting an appropriate motor response by activating effectors through cranial and spinal nerves. Stimulation of the effectors causes muscles to contract and glands to secrete.

cytosol

Fluid portion of cytoplasm

Nodes of ranvier

Gaps in a myelin sheath - Each Schwann cell wraps one axon segment between two nodes of Ranvier. Myelinated nodes are about 1 mm in length and have up to 100 layers.( wont ask) - The amount of myelin increases from birth to maturity, and its presence greatly increases the speed of nerve conduction. Diseases like Multiple Sclerosis result from autoimmune destruction of myelin.

Two types of electrical signals to neurons

Graded potentials and action potentials

Unipolar neurons

Have dendrites and one axon that are fused together to form a continuous process that emerges from the cell body. Function as sensory receptors. Detect touch, pressure, pain, or thermal stimuli.

Neurons

Have the ability to respond to a stimulus and convert it into an action potential. They are the real "functional unit" of the nervous system, forming complex processing networks within the brain and spinal cord that bring all regions of the body under CNS control.

cytosol

Intracellular fluid

Resting membrane potential

Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?

Enteric nervous system

Is the nervous system that is found in the digestive tract: it innervates smooth muscle and glands.

3 types of active, gated channels

Ligand-gated Voltage-gated Mechanically gated

Astrocytes

Make up half of all neural volume and are star-shaped. ii. They possess numerous projections with bulbous ends that cling to neurons and capillaries therefore they serve as connections between neurons and blood/nutrient supply. This is called the blood-brain barrier. iii. Astrocytes control the chemical environment around neurons by regulating ions, nutrients, dissolved gas concentrations, and hormones. They also absorb and recycle neurotransmitters that cannot be broken down and they form scar tissue after injury.

Neurolemma

Outer nucleated cytoplasmic layer of the Schwann cell which encloses the myelin sheath.

Integrative function

PROCESSES sensory information by analyzing it and making decisions for appropriate responses - an activity known as integration

nerve

-is a bundle of axons and their sheaths

3 Functions of the nervous system

1. Sensory function. 2. Integrative function 3. Motor function

The autonomic nervous system consists of

1. sensory neurons that convey information from autonomic sensory receptors, located primarily in visceral organs such as the stomach and lungs, to the CNS 2. Motor neurons that conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands.

Sympathetic division

A branch of the autonomic nervous system and prepares the body for quick action in emergencies; fight or flight; busiest when frightened, angry, or aroused; increases heart rate, increases breathing rate, enlarges pupils, stops digestion; connects to all internal organs; sudden reaction

Multiple sclerosis

A chronic disease of the central nervous system marked by damage to the myelin sheath. Plaques occur in the brain and spinal cord causing tremor, weakness, incoordination, paresthesia, and disturbances in vision and speech

parasympathetic division

A division of the autonomic nervous system; it returns the body to its resting state.

Axon

A long projection off the cell body of a neruon down which an action potential can be propagated.

Neuron

A nerve cell; the basic building block of the nervous system.

Active channels open in response to

A stimulus

Myelin sheath

A white, fatty covering wrapped around the axons of some neurons that increases their communication speed.

Trigger zone

Nerve impulses arise here. From which they travel along the axon to their destination.

Neuroglia in PNS

Satellite and Schwann

KNOW 6 types of neuroglia

Satellite, Schwann, astrocytes, Oligodendrocytes, microglia, Ependymal cells

Synaptic vesicles

Secretory vesicle in the presynaptic terminal containing neurotransmitter substances

Functional classification of neurons. 3 types

Sensory (afferent) Motor (efferent) Interneurons

Astrocytes

Star-shaped cells have many processes and are the most numerous.

Neuroglia (test) exact function

Support neurons by - forming the blood brain barrier - forming the myelin sheath (nerve insulation) around neuronal axons - making the CSF that circulates around the brain and spinal cord - participating in phagocytosis

Varicosities

Swellings along nerve fibers that have synaptic vesicles from which neurotransmitters are released.

Nerve

a bundle of hundreds of thousands of axons plus associated C.T. and blood vessels that lies outside the brain and spinal cord.

sensory receptor

a structure of the nervous system monitors changes in the external or internal environment. such as touch receptors in the skin and photoreceptors in the eye and olefactory receptors in the ear.

Motor or efferent neurons

convey action potentials away from the CNS to effectors (muscles and glands) in the periphery through cranial or spinal nerves. Most are multipolar

STructural classification is based on? (test)

the number of processes (axons or dendrites) extending from the cell body.

Axon terminal (telodendria)

they interact with the dendritic tree of neurons "downstream"

Soma function

where the signals from the dendrites are joined and passed on