Nerves, Neurones and Synapses

how many neurones in human brain

roughly 100 million

frontal lobe roles

reward, motivation, motor cortex, ‘higher’ func.

pariental lobe roles

speech

somatosensory cortex

occipital lobe roles

visual cortex

temporal lobe roles

memory info

processing

sensory info

emotions?

central nervous system includes…

brain

spinal chord

peripheral nervous system includes…

somatic

enteric

autonomic → sympathetic + parasympathetic

nerve vs neurons

nerves are bundles of neurones

bioelectricity

membrane potential, result of ion gradient

excitable cells

cells’ membrane potential changes in response to stimuli

nerve impulses def.

changes in membrane potential that travel down nerves

which ion has higher conc. in extracellular

Na+

Cl-

Ca2+

which ion has higher conc. in intracellular

K+

membrane potential can be calculated how?

NERNST EQUATION

soma

cell body in neurones

during depolarisation

Na+ VG ch open

during repolarization

K+ VG vh open

during refractory period

re-establishment of resting potential

Na+ / K+ VG ch exchange

resting potential is…

-70 mV

threshold is…

-55 mV

action potential is…

+40 mV

measuring membrane potential

Vm = Vi - Vo

myelination in the CNS

Oligodendrocytes

node of ranvier

mitochondrion in axoplasm

microtubule

soma of oligodendrocytes

myelination in PNS

Schwann cells

node of ranvier

myelin sheath

sodium potassium pump

2K+ in, 3Na+ out

AP reaching end of neurone

Na+ VG ch (AP) → Ca2+ VG ch open→ influx of Ca2+→ neurotransmitters, synapse

Excitatory Neurotransmitters

Glutamate

monoamines

acetylcholine

Inhibitory Neurotransmitters

GABA

glycine

endorphins

Neuromodulators eg.

neuropeptides

endocannabinoids

Ionotropic receptors

faster

ligand gaited ion channel

not G-coupled

Glycine

metabotropic receptors

slower, more diverse effects

G-coupled

histamine

how to determine if neurone fires?

sum of all synaptic inputs on the same dendrite, mix and match of excitatory and inhibitory

glial cells ?

• 50-80% of brain

• astrocyte

• microglia

• oligodendrocyte

• supporting roles

• CSF prod.

Astrocyte

Support

BBB

Communication

NT waste

Scar

Microglia

brain specific immunity

macrophage

mediates neuroinflammation

Neuromuscular junction

Ach neurotransmitter

acetylcholinesterase

ionotropic

controls voluntary muscles → can be overridden & override voluntary control

ascending tracts in SNS

relay info from spinal chord to sensory cortex

descending tracts in SNS

relay info from motor cortex to spinal chord

sensory neurones relay info to …

spinal chord / brain

motor neurones

relays info from spine to muscle (skeletal)

exits spine via ventral root

Botulinum toxin

inhibits acetylcholine secretion

flaccid paralysis

Organophosphates

inhibits acetylcholinesterase

muscle spasms

Myasthenia Gravis info

autoimmune disease

antibodies → Ach receptors + muscle receptor tyrosine kinase

Myasthenia Gravis symptoms

double vision

ptosis

Myasthenia Gravis treatment

cholinesterase inhibitors

reflex arc

receptor → afferent neurone → integration center → efferent neurone → effector organ

Reflexes info

initiation of voluntary movements

controlled by spine

Muscle spindles are…

specialised muscle fibres

they are surrounded by a capsule inside skeletal muscle, proprioceptors sense muscle length and activate sensory neurones.

Stretch relfex…

increased muscle tension, to counter stretching

proprioceptors

between muscle and tendon, sense tension & activate sensory neurones-type iB

joint capsule

Autogenic inhibition

Type iB axon synapse → inhibitory spinal interneurones

inhibiting alpha

reducing muscle contraction

regulates muscle tension

Inhibitory interneurones do..

stretch reflex

reciprocal inhibition

Brain control of movement

• basal ganglia

• thalamus

• cerebellum

• motor cortex

• somatosensory cortex

• spinal chord

crossed extensor reflex

maintain balance during ipsilateral movement

painful stimulus on first foot causing withdrawral

Basal ganglia

center for controllling and initiating voluntary movement

cerebellum

controls complex series of movements

inhibited in ethanol intoxication

highly complex