1A03 - NEUROTRANSMISSION + SPINAL CORD + ANS

How AP travels

How AP travels

1. AP in communicating neurons stimulate GP in receiving neuron that summate at trigger zone

2. AP are propagated down axon terminal

3. AP result in communication of neuron with its target

Types of Propagation

continuous and saltatory

Continuous Conduction

slow conduction that occurs in unmyelinated axons

Saltatory Conduction

rapid conduction that occurs at nodes of ranvier

Factors Impacting Propagation Speed

• axon diameter

• amount of myelination

• temperature

Nerve Fiber Types

type A, type B, type C

Type A Nerve Fibers

• large diameter

• myelinated

• 15-120 m/s

• in motor neurons

Type B Nerve Fibers

• medium diameter

• lightly myelinated

• 3-15 m/s

• sympathetic nervous system

Type C Nerve Fibers

• small diameter

• unmyelinated

• 2 m/s or less

• parasympathetic nervous system

Synapse

junction between cells that allows one to communicate with another

Presynaptic Cell

passes signal

Postsynaptic Cell

receives signal

Gap Junction

gap between cells; 2nM

Connexons

• tubular proteins that attach cells

• creates opening between cytosol

Synaptic End Bulb/Pre-Synaptic Terminal

end of axon

Synaptic Cleft

space between two connecting neurons where neurotransmitters are released

Electrical Synapse

• in cardiac + smooth muscle

• ions move physically

• AP spreads through cell between connexons

Chemical Synapse

• no direct transfer

• rely on neurotransmitters to relay info

• presynaptic terminals release neurotransmitters from synaptic vesicles

Removal of Neurotransmitters

diffusion, enzymatic degradation, uptake by cells

EPSP (excitatory postsynaptic potential)

• depolarization

• stimulatory response

IPSP (inhibitory postsynaptic potential)

• hyperpolarization

• inhibitory response

Spatial Summation

adding independent GP together from different neurons

Temporal Summation

when two AP arrive in very close succession at single terminal

Spinal Cord

• long structure

• supported by nervous tissue

• must curve to maintain position in vertebral column (surrounded by meninges)

• from foramen magnum to L2

Cervical Enlargement

C4-T1

Lumbosacral Enlargement

T1-T12

Cauda Aquina

nerves that come out of bottom of spinal cord

Filum Terminale

• extension of pia mater

• stops movement in superior direction

• anchors spinal cord to coccyx

Conus Medullaris

inferior end of spinal cord

Vertebrae

• bony structures surrounding spinal cord

• form vertebral column

Vertebral Foramen

• faces superior/inferior

• opening near spiny processes

Vertebral Canal

• connection of vertebral foramen

• when spinal cord is located

Intervertebral Foramina

• spaces between vertebrae

• where spinal cord exits vertebral canal and extend to periphery

Protective Layers of Spinal Cord (Superficial to Deep)

• dura mater

• epidural space

• periosteum

• subdural space

• arachnoid mater

• subarachnoid space

• pia mater (denticulate ligaments and filum terminale)

Inner Gray Matter of Spinal Cord

• 3 horns

• connected by commissures

• each level has rootlets

Rootlets

• enter spinal cord

• part of PNS

• ventral and dorsal

Posterior Horn (Gray Matter)

• sensory axons

• interneurons combine with nerve tract in white matter

Lateral Horn (Gray Matter)

• small

• associated with ANS, thoracic and lumbar regions

Anterior Horn (Gray Matter)

• 'motor horn'

• cell bodies for somatic neurons

• largest

Ventral Root

exit of motor neurons

Dorsal Root

entrance of sensory neurons

Dorsal Root Ganglion (DRG)

• associated with the dorsal horns

• cell bodies of sensory neurons are located here

3 CT Layers Around Myelinated Axons

endonerium, epinerium, perinerium

Dorsal Rami

• posterior

• deep back muscles + vertebral column movements

Ventral Rami

• anterior

• cervical, brachial, lumbar, sacral, coccygeal

Cervical Plexus

• C1 to C4

• superficial neck structures, neck skin, posterior part of head

• phrenic nerve

Phrenic Nerve

• cervical plexus

• innervates diaphragm

• C3 to C5

Brachial Plexus

• C5 to T1

axillary: deltoid/teres minor

radial: post. part of arm/forearm

musculotaneous: forearm flexors

ulnar: forearm/most of hand muscles

median: anterior forearm/hand muscles

Lumbar Plexus

• L1 to L4

• obturator and femoral nerves

Sacral Plexus

• L4 to S4

• tibial and common fibular

Coccygeal Plexus

• S5 to Co.

• pelvic floor muscle

• sensory info from skin

Routes of Sympathetic Axons

• spinal nerve

• sympathetic nerve

• splanchnic nerve

• adrenal medulla

Chain Ganglia

• postganglionic cell bodies close to spinal cord

• 2 chains on each side of vertebral column

Collateral Ganglia

• postganglionic cell bodies close to effectors

Sympathetic Division

• thoracolumbar

• lateral horns

• T1 to L2

Parasympathetic Division

• craniosacral

• cell bodies in lateral gray horn

• S2 to S4

• associated with nuclei of cranial nerves

Enteric Division

• innervation to digestive tract

• plexuses with nerve cell bodies

• 3 points of nervous input into digestive tract

Sympathetic neurons create ______________ neurotransmitters

• cholinergic (preganglionic)

• adrenergic (postganglionic)

Parasympathetic neurons always create __________ neurotransmitters

cholinergic

Nicotinic Receptors

• cholinergic

• excitatory

• open Na+ channels

• on cell bodies of postganglionic neurons + neurotransmitters and neuromuscular junction

Muscarinic Receptors

• cholinergic

• excitatory or inhibitory

• G-protein signalling

• on membrane of parasympathetic effectors

Adrenergic Receptors

• alpha and beta receptors

• excitatory (A1/B1) or inhibitory (A2/B2)

Parasympathetic Functions

• SLUDD

• 3 decreases

Sympathetic Functions

• E situations

• increases (5)

• pupil dialation

• decreased blood flow to non-essential organs