Toth Neuroanatomy I

Central Nervous System

• brain and spinal cord

• integration and control system

  • interprets sensory input and dictates motor output

Peripheral Nervous System

• portion of nervous system outside CNS

• consits mainly of nerves that extend from brain and spinal cord

  • Spinal

  • Cranial

Spinal Nerves

to and from spinal cord

Cranial Nerves

to and from brain

enteric nervous system

walls of gastrointestinal tract also contain neurons called the enteric nervous system

PNS two divisions:

• Sensory (afferent) division

• Motor (efferent) division

Sensory (afferent) division’s divisions:

• somatic sensory fibers

• visceral sensory fibers

somatic sensory fibers:

• convey impulses from skin, skeletal muscles and joints to CNS

visceral sensory fibers:

• convey impulses from visceral organs to CNS

Motor (efferent) division:

• transmits impulses from CNS to effectors

  • muscles and glands

Motor (efferent) division two divisions:

• somatic nervous system

• autonomic nervous system

nervous tissue two principle cell types:

• neuroglia

• neurons

neuroglia:

• glial cells

• small cells that surround and wrap delicate neurons

neurons:

• nerve cells

• excitable cells that transmit electrical signals

FOUR MAIN NEUROGLIA SUPPORTS CNS neurons

• astrocytes

• ependymal cells

• microglial cells

• oligodendrocytes

Astrocytes

• most abundant

• versatile

• higly branched of glial

Astrocytes Functions:

• support and brace neurons

• play role in exchanges between capillaries and neurons

• guide migration of young neurons

• control chemical enviorment around neurons

• respond to nerve impulses and neurotransmitters

• participate in information processing in brain

astrocyte

microglial cells

• clean up

• small, ovoid cells with thorny processes that touch and monitor neurons

• migrate toward injured neurons

• can transform to phagocytize microorganisms and neuronal debris

microglial

ependymal cells

• range in shape from squamous to columnar

• may be ciliated

  • cillia beat to circulate CSF

• lines the central cavities of the brain and spinal cord

• form permeable barrier between CSF in cavities and tissue fluid bathing CNS cells

ependymal cells

oligodendricytes

• produce myelin sheath

• branched cells

• processes wrap CNS nerve fibers, forming insulating myelin sheaths in thicker nerve fibers

Neuroglia of the PNS two types:

• satelite cells

• schwann cells

satelite cells

• surround neuron cell bodies in PNS

• function similar to astrocytes of CNS

schwann cells (neurolecmmocytes)

• surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers

  • similar function as oligodendricytes

• vital to regeneration of damaged peripheral nerve fibers

Neurons:

• nerve cells

• are structural units of nervous system

• large, highly specialized cells that conduct impulses

• all have a cell body and one or more processes

special characteristics of neurons

• extreme longevity (lasts a persons lifetime)

• amitotic, with a fe exceptions

• high metabolic rate: requires continuous supply of oxygen and glucose

1

dendrites (receptive region)

2

cell body (biosynthetic center and receptive region)

3

axon terminals (secretory region)

4

nucleus

5

nucleolus

6

Chromatophilic substance (rough ER)

7

axon hillock

8

initial segment of axon

9

axon (impulse - generating and conducting region)

10

myelin sheath gap

11

schwaan cell

12

terminal branches

phosolipid head

hydrophilic

phosolipid tails

hydrophobic tail

Chemically gated ion channels

• open in response to binding of the appropriate neurotransmitter

• open and close

  • depends on if there is a neurotransmitter present

Chemically gated ion channels - state when theres no receptor

• closed

  • K+ stays inside the cell and cant pass through

  • Na+ stays outside the cell and cant pass through

Chemically gated ion channels - state when theres a receptor

• open

  • Na⁺ moves into the cell

  • K⁺ may move out of the cell (depending on the channel type)

volage- gated ion channels

• open in response to changes in membrane potential

volage- gated ion channels - closed

• Closed: when the membrane is at resting potential

Na+ volage- gated ion channels - closed

• Na⁺ cannot enter through these channels

  • However, Na⁺ still has a strong desire to move INTO the cell (because:

  • higher concentration outside

  • negative inside attracts it)

K+ volage- gated ion channels - closed

• K⁺ can still move through leak channels

• So K⁺ slowly diffuses OUT of the cell

volage- gated ion channels - open

• Open: when the voltage across the membrane changes enough

Na+ volage- gated ion channels - open

• Na⁺ rushing in = depolarization (cell becomes positive)

• Voltage-gated Na⁺ channels open first

• Na⁺ rushes INTO the cell very quickly

• This happens because:

  • high concentration outside

  • negative inside attracts Na⁺

👉 So: massive Na⁺ influx → inside becomes more positive

K+ voltage- gated ion channels - open

• Shortly after, voltage-gated K⁺ channels open

• K⁺ then moves OUT of the cell

👉 So: K⁺ leaves, but slightly later than Na⁺ enters

K⁺ leaving (after) = helps bring the cell back down

resting membrane potential

• generating a resting membrane potential depends on:

1. differences in K+ and Na+ conc. inside and outside cells and,

2. differences in permeability

Na and K resting membrane potential

• Na+ conc is higher outside the cell

• K+ conc is higher inside the cell

what maintains the conc. gradient

Na+ and K+ puumps maintain the conc. gradients of Na+ and K+ across the membrane