neuron structure and function

what is a neuron

fundamental, functional unit of the nervous system

neuronal cell membrane

hydrophobic, binds together cytoplasm

neuron nucleus

chromosomes for protein production

neuron ER

isolate, modify, store, transport proteins and lipids

rough ER

ribosomes for protein synthesis

smooth ER

lipid synthesis

lysosomes

digest compounds, make glucose, transport

golgi apparatus

stores formed proteins and lipids

microtubules

axonal transport, relay neurotransmitters down axis

functions of axons

transmit info via propagation of AP, transport metabolically important materials to and from cell body

anterograde

from the body to axon

retrograde

from axonal end back to cell body

myelinated axons

transport quicker, schwann cells myelinate

unmyelinated axons

schwann cells provide trophic support

electrostatic force

like charges repel

diffusion force

ion more from high to low concentration

ligand gated ion channel

ligand attached to receptor and opens channel

mechanically gated ion channel

opens in response to pressure or stretch

voltage gated ion channel

opens when membrane potential reaches threshold

depolarization

voltage increases, excitatory event, becomes less negative inside

hyperpolarization

voltage decreases, inhibitory event, become more negative inside

AP mechanism

excitatory stimulus, influx of Na

reaches 30mV, Na channels close, K+ diffuses out

inside becomes hyperpolarized, active pump starts working

resting membrane potential reached

what increases speed of propagation

myelinated axon, larger diameter axons

functions of myelin sheath

electrical insulator, accumulation of charge, speeds up conduction

motor nerve fibers

myelinated, muscle fibers

larger sensory nerve fibers

myelinated, touch, vibration, position, perception

medium sensory nerve fibers

thinly myelinated, cold perception, pain

small sensory nerve fibers

unmyelinated, warmth perception, pain

autonomic nerve fibers

thinly or unmyelinated, heart rate, blood pressure, sweating

direction of information flow for chemical synapses

presynaptic neuron to postsynaptic neuron

synapse sequence

AP arrives, Ca influx exocytosis of vesicles, binding of neurotransmitters, NA influx, AP generation

excitatory neurotransmitters

glutamine, acetylcholine

inhibitory neurotransmitters

GABA

diffusion

away from synapse

reuptake

neurotransmitter reenters presynaptic axon terminal

enzymatic destruction

inside terminal cytosol of synaptic cleft

desensitization

neurotransmitter becomes inactive

synaptic fatigue

presynaptic vesicles released at faster rate than reuptake can recycle them

purposes of nervous system

coordinates body activities, voluntary and involuntary movement, cognition, respond and adapt to internal or external demands

spinal cord functions

conveys sensory input, controls motor output and function

parts of brainstem

midbrain, pons, medulla

midbrain

eyes and auditory

pons

reflex actions, chewing and tasting

medulla

heart rate, respiration, blood pressure

diencephalon

processing center, thalamus and hypothalamus

thalamus

send sensory info to cerebrum

hypothalamus

regulates temp, sleep, appetite, thirst, bv dilation and constriction

spinal nerves

31 pairs, sensory and motor

cranial nerves

12 per side

number of cervical nerves

8

number of thoracic nerves

12

number of lumbar nerves

5

number of sacral nerves

5

number of coccygeal nerves

1

sympathetic nervous system

heart rate

parasympathetic nervous system

bowel and bladder function

structure of spinal nerves

roots, trunks, divisions, chords, branches

connective tissue layers of spinal nerve

epineurium, perineurium, endoneurium

sensory info to spinal cord

mechanical stimulus creates electrical impulse

one end of dorsal root ganglion connected to receptor

enters spinal cord via dorsal horn, relays info

spinal motor neurons

anterior horn cells, alpha or gamma, in gray matter

motor reflex process

axons leave spinal cord via ventral roots

innervate skeletal muscles

motor unit

single alpha motor neuron and all muscle fibers it innervates

one motor neuron can innervate…

many muscle fibers

one muscle fiber receives innervation from…

one motor neuron