Lecture 16 - functional information flow

Question 1

Types of information transmitted

Answer 1

Somatic = the stuff that we are aware of, have control over

Autonomic = the stuff we are not aware of, have no control over

Question 2

Somatic

Answer 2

Somatic = the stuff that we are aware of, have control over

Voluntary muscle control = somatic efferent (motor)
Sensory information we are awarer of = somatic afferent

Question 3

Autonomic

Answer 3

Autonomic = the stuff we are not aware of, have no control over

Involuntary muscle control e.g. heartbeat = autonomic efferent (motor)
Sensory information that we do not know about e.g. blood pressure = autonomic afferent (sensory)

Question 4

Somatic efferent (motor) division

Answer 4

Voluntary control (muscle)

Two neurons between the brain and the effector
1- upper motor neuron - cell body in the brain, axon in the spinal cord (then makes a synapse with another neuron called the lower motor neuron)
2- lower motor neuron - cell body in the spinal cord, axon in spinal nerve ( extends its axon out of the CNS and into the PNS and makes synaptic contact onto a skeletal muscle)

Effectors = skeletal muscle fibres (control the contraction of these fibres)

Question 5

Effectors

Answer 5

Things the nerves go to and control

Question 6

Anatomical organisation of the somatic efferent (motor) division

Answer 6

1- upper motor neuron - cell body in brain, axon in spinal cord (myelinated - by oligodendrocytes because it is the CNS)
2- lower motor neuron - cell body in spinal cord, axon in spinal nerve (myelinated - by Schwann cells because it is the PNS)

Both are myelinated to ensure that the conduction of this signal is very fast

Presynaptic cell is the lower motor neuron and the post synaptic cell is the effector (therefore this is a neuromusclular junction). The neurotransmitter released into the synaptic cleft is acetylcholine (ACh)

Question 7

Autonomic (efferent) nervous system

Answer 7

Involuntary control (motor)

Two divisions = sympathetic and parasympathetic

Three neurons between the brain and the effector (features shared between the two division) …
Neuron #1- cell body is in the brain, Axon is in the brain or spinal cord (CNS)
Neuron #2 - Cell body is in the brain or spinal cord (CNS), axon is in the PNS
Neuron #3 - cell body is in the PNS, axon is in the PNS

Effectors - smooth muscle, cardiac muscle, glands and adipose (fat) tissue

Question 8

Autonomic (efferent) nervous system - basic anatomical features

Answer 8

Just Neuron #2 and #3

Neuron #2 - cell body is in the CNS and the axon extends into the PNS. It is myelinated. Synapses in the autonomic ganglion and it is the preganglionic neuron

Neuron #3 - cell body is in the PNS in the autonomic ganglion. The axon extends in the PNS to the effector organ. It is unmyelinated and synapses onto the effector organ. It is the post ganglionic neuron (the entirety of this neuron is in the PNS)

There is no loss in neuron #3 being unmyelinated. This is because the axon are very tiny in diameter and when axons are small like this myelin doesn’t actually help them conduct any faster

Question 9

Autonomic ganglion

Answer 9

An autonomic ganglion is a cluster of nerve cell bodies (a ganglion) in the autonomic nervous system.

Question 10

Autonomic (efferent) nervous system - synaptic neurotransmitters

Answer 10

Neuron #2 - the neurotransmitter released is acetylcholine (ACh)

Neuron #3 - the neurontransmitter released is ACh (parasympathetic) or norepinephrine (sympathetic)

Question 11

Subdivisions of the autonomic (efferent) nervous system

Answer 11

Sympathetic and parasympathetic

Question 12

Sympathetic

Answer 12

Prepares the body for acute/stress responses. It is the fight or flight system.

Effects include:
Increased heart rate
Constricting of blood vessels to skin and internal organs (increased blood flow to the muscles) 
Decreased gastric motility 
Decreased salivation 
Increased pupil size 
Increased sweating

Question 13

Parasympathetic

Answer 13

Prepares the body for restful situations. The rest and digest systems.

Effects include:
Decreased heart rate
Increased gastric motility 
Decreased pupil size 
Increased salivation

Question 14

Structural and neurotransmitter differences between sympathetic and parasympathetic nervous systems (neurons #2 and #3)

Answer 14

Sympathetic
The preganglionic neuron (#2) has a short axon. It releases ACh in the synaptic cleft and the autonomic ganglion is close to the CNS. The post ganglionic neuron (#3) has a long axon and releases norepinephrine (NE) onto the effector.

Parasympathetic
The preganglionic neuron (#2) has a long axon. It releases ACh into the synaptic cleft and the autonomic ganglion is distant from the CNS (closer to the effector). The post ganglionic neuron (#3) has a short bacon and releases ACh onto the effector.

Question 15

Sympathetic nervous system - exit from CNS and ganglia

Answer 15

Axon of the preganglionic neurons (neuron #2) leaves CNS at thoracolumbar levels (spinal cord - T1-12 and L1,L2 only)

Axon extends a short distance

Synapse and cell body of the post ganglionic neuron (neuron #3) are in sympathetic ganglion

Question 16

Sympathetic chain ganglia

Answer 16

21-23 pairs

These are alongside the vertebral column

It is the place where preganglionic (neuron #2) axons synapse onto the post ganglionic neuron (#3) input zone.

Contain cell bodies that utilise norepinephrine (all other synapses are ACh except where the sympathetic post ganglionic neurons make contact with the effector cells (NE)

Ones close to the vertebral column and in this ganglia are the cell bodies of the POST-GANGLIONIC neurons in the sympathetic nervous system

Question 17

Parasympathetic nervous system - exit from CNS and ganglia

Answer 17

Axon of preganglionic neuron (neuron #2) leaves the CNS at cranial (brainstem) OR sacral (spinal cord - sacrum region) levels (sometimes called the craniosacral nerves)

Axon of preganglionic neurons is long

Synapse and post-ganglionic neuron (neuron #3) cell body in ganglion in or near the effector organs

Axon of postganglionic neuron (#3) is short (makes a synapse right on the effector)

Question 18

Preganglionic neuron (#2) in sympathetic vs parasympathetic

Answer 18

Preganglionic neurons are myelinated regardless of system

Cell body location in CNS
Sympathetic - Thoracolumbar (spinal cord T1-L2)
Parasympathetic - Craniosacral (brain stem and sacral spinal cord)

Synapse in
Sympathetic - sympathetic chain or collateral (sympathetic ganglia which lie between the sympathetic chain and the organ of supply) ganglion
Parasympathetic - parasympathetic ganglion or near effector

Length of fibres
Sympathetic - relatively short
Parasympathetic - relatively long

Neurotransmitter
Sympathetic - ACh
Parasympathetic - ACh

Question 19

Post ganglionic neuron (#3) sympathetic vs parasympathetic

Answer 19

Postganglionic neurons are unmyelinated regardless of system

Post ganglionic parasympathetic neuron has its cell body residing distant from the CNS (close to the effector

Cell body location in CNS
Sympathetic - sympathetic chain or collateral ganglion
Parasympathetic - parasympathetic ganglion in or near effector

Length of fibres
Sympathetic - relatively long
Parasympathetic - relatively short

Neurotransmitter
Sympathetic - noradrenaline (most)
Parasympathetic - ACh

Question 20

What neurotransmitter is used by somatic efferent neuron?

Answer 20

Acetylcholine

Question 21

If you were told that your craniosacral nervous system were activated, that means you are …..

Answer 21

Relaxed as it is the parasympathetic nervous system which is the rest and digest response

Question 22

Afferent sensory neurons

Answer 22

Afferent sensory neurons contain afferent sensory information that goes up the neurons into the spinal cord and up to the brain

Question 23

Efferent sensory neurons

Answer 23

Efferent motor neurons contain information from the brain and spinal cord being sent out into the periphery. Can be spilt into two groups… Somatic nervous system (voluntary) and the autonomic nervous system (involuntary). Somatic nervous system goes to innervate things like our muscles which we need to think and about and decide in order to contract them. The autonomic system can be divided into the parasympathetic nervous system and the sympathetic nervous system and these innervated things like the heart and the glands