Anatomy Lecture Notes Chapter 12

A. functions of

1. monitors changes in internal and external environment

2. processes and interprets sensory input

3. controls effector organs (muscles and glands)

B. organization of nervous system (NS)

1. components

CNS PNS cranial spinal nerves

2. organization

afferent/sensory = carrying information toward the CNS efferent/motor = carrying information away from the CNS somatic - skeletal muscles, bones and skin visceral - cardiac muscle, smooth muscle and glands

CNS

PNS

sensory motor

somatic visceral somatic visceral

receptors effectors

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Anatomy Lecture Notes Chapter 12

C. tissue

1. = specialized to transmit electrical signals extreme longevity do not divide high metabolic rate

2. neuroglia (supporting cells, glial cells) non-excitable function is to support the neurons make up 50% of brain mass ratio in brain is about 10 glial cells per can divide to replace themselves

D. neurons

1. structure

a. cell body//perikaryon nucleus chromatophilic bodies (rER and ribosomes) neurofibrils

b. processes/fibers - extensions of the cell body

: most neurons have many dendrites enlarge the surface area of the cell receive signals from other neurons and send it to the cell body

: one per neuron arises from in most neurons axonal transport delivers materials from cell body to distant parts of cell branches are called collaterals end in smaller branches called telodendria or terminal branches at the ends of the telodendria are small enlargements called axon terminals or synaptic knobs; they contain neurotransmitters axons carry signals away from the cell body

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Anatomy Lecture Notes Chapter 12

2. structural classification - number of processes:

a. multipolar - most common (>99%)

b. bipolar - occur in sensory pathways

c. (pseudo)unipolar - sensory neurons

3. functional classification - direction of transmission

a. afferent/sensory mostly pseudounipolar, some are bipolar cell bodies are in sensory ganglia of spinal or distal end is either a sensory or with a sensory receptor cell

b. efferent/motor multipolar cell bodies in CNS or motor ganglia with effector cells

c. entirely within CNS 99.98% of all neurons most are multipolar

CNS

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Anatomy Lecture Notes Chapter 12

E. glial cells / neuroglia

1. (CNS) most abundant type processes wrap neurons or capillaries control ion levels near neurons capture and recycle neurotransmitters

2. (CNS) smallest and least abundant derived from monocytes during development phagocytize pathogens and dead cells

3. ependymal cells (CNS) simple epithelium lines brain ventricles and spinal cord central canal physical barrier between cerebrospinal fluid (CSF) and brain tissue fluid help make and circulate CSF

4. (CNS) cell processes produce in CNS

5. satellite cells (PNS) surround cell bodies in sensory ganglia

6. Schwann cells (PNS) form myelin in PNS

F. myelin sheath made of lipoprotein surrounds some axons many layers of cell membrane wrapped around axon electrically insulates membrane of axon

1. PNS (Schwann cells) incomplete at birth formation continues for first year

a. - outer membrane and cytoplasm external to myelin sheath

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Anatomy Lecture Notes Chapter 12

b. gaps between adjacent Schwann cells are nodes of Ranvier (1mm apart) no myelin or neurilemma at node nerve signals "jump" from node to node myelin speeds signal transmission

2. CNS (oligodendrocytes) one 's processes wrap several axons nodes are farther apart than in PNS

G. chemical synapses

synapse = point of communication between two neurons

1. presynaptic neuron axon terminals contain neurotransmitter in synaptic vesicles

synaptic cleft or gap = space between presynaptic and postsynaptic neurons

2. postsynaptic neuron membrane contains: receptors for neurotransmitter ion channels controlled by the receptors

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Anatomy Lecture Notes Chapter 12

H. basic multi-neuronal structures

1. CNS

a. gray (not grey) matter consists mostly of cell bodies cortex is a thin layer of neuron cell bodies (gray matter) covering the outside of parts of the cerebrum and cerebellum a nucleus is a clump of neuron cell bodies (gray matter) located in the brain b. consists mostly of myelinated axons a tract is a bundle of axons (myelinated) in the brain or spinal cord

CNS

2. PNS

a. nerve = bundle of axons surrounded by c.t. each axon is surrounded by an made of loose c.t. axons are grouped into fascicles by the the surrounds all fascicles and is made of tough fibrous c.t.

b. /ganglia - clump of neuron cell bodies in PNS, surrounded by c.t. can be either sensory or motor

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Anatomy Lecture Notes Chapter 12

I. reflex = rapid, automatic, unlearned, predictable motor response to a reflexes are motor responses caused by a hard-wired neural circuit reflex arc = pathway for a reflex

1. receptor - detects changes in environment

2. afferent neuron - carries signals from receptor to CNS

3. integration center - one or more synapses in CNS incoming sensory signals elicit outgoing motor signals

4. efferent neuron - carries signals from CNS to effectors

5. effector - organ that produces reflex response (muscle or gland)

J. damaged neurons cannot be replaced

1. neuroblasts stop being produced during fetal development

2. new cells generated

a. in hippocampus from ependymal cells

b. in olfactory epithelium

3. damaged nerve processes can regenerate if the cell body is intact and there is a path of Schwann cells for it to follow (this happens in PNS only)

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