HUBS Module 3 - Nerve and muscle

Explain integration and coordination in nervous system

Integration is sensing environment and coordination is responding to it. E.g. integration is feeling the pain of stepping on something sharp and coordination is responding to it by moving your foot

What are the two parts of the nervous system

Central nervous system and peripheral nervous system

What does the CNS consist of

Brain and spinal cord (made of neurons and glia)

What does PNS consist of

Peripheral nerves and ganglia (made of neurons and glia)

What are two features of neurons

1. Cells specialised for transmission of information
2. Four morphological types

What is the basic function of glial cells

Support for neurons

Two features of dendrites

Recieve input

Send info to cell body

Two features of neuron cell body

Contains nucleus and organelles

Sums input

Two features of axon

Carries electrical impulses

May or may not be myelinated

Two features of axon terminals

End of the axon

Neurotransmitter release

Label

What is nucleus (nervous system)

Group of cell bodies in the CNS

What is a tract (nervous system)

Bundle of axons in the CNS

What is grey matter (nervous system)

Group of cell bodies in cerebral cortex or spinal cord in the CNS

What is white matter (nervous system)

Bundle of axons in cerebral cortex or spinal cord in the CNS

What is a ganglion (nervous system)

Group of cell bodies in the PNS

What is a nerve (nervous system)

Bundle of axons in the PNS

Input zone in neuron (structure and function)

Dendrites and cell body

It recieves CHEMICAL signals from other neurons

Summation zone in neuron (structure and function)

Axon hillock

It summates inputs

Conduction zone in neuron (structure and function)

Axon

Carries ELECTRICAL signals between brain areas, to and from spinal cord, or from peripheral sensory receptors to effector cells

Output zone in neuron (structure and function)

Axon terminals

Contact with input zone of other neurons or effectors

Release of neurotransmitter (chemical signal)

Four morphological types of neurons

Multipolar

Bipolar

Unipolar

Anaxonic

Multipolar neurons

Multiple processes emanate from the cell body

Bipolar neurons

Two processes emanate from the cell body

Unipolar neurons

One process emanates from the cell body, then branches into dendrite and axon

Anaxonic neurons

No distinct axon, all processes look alike

Five basic types of glia

Astrocytes (CNS)

Microglia (CNS)

Ependymal cells (CNS)

Oligodendrocytes (CNS)

Schwann cells (PNS)

Astrocytes functions

Supply nutrients to neurons

Ensheath blood capillaries

Injury response

Microglia functions

Immune cells of the CNS

Engulf microorganisms and debris

Ependymal cells functions

Line fluid filled spaces of brain and spinal cord

Have cilia to circulate CSF

Oligodendrocytes functions

Support CNS nerve fibres

Ensheath them with myelin

Schwann cells functions

Support PNS nerve fibres

Ensheath them with myelin

Myelin and its function

Layer of lipid (fat) wrapped around an axon to increase conduction velocity

What are nodes of ranvier

Gaps between the myelin on axons to further increase conduction velocity

What is a synapse

A junction between neurons that communication occurs through

Pre-synaptic neuron

Neuron before synapse

Post-synaptic neuron

Neuron after synapse

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Afferent definition

Information that goes into the brain

Efferent definition

Response that comes out of the brain

What is somatic in the nervous system

The stuff we are aware of and have control over

What is autonomic

The stuff we are not aware of and have no control over

What is somatic efferent

Voluntary muscle control

What is somatic afferent

Sensory information we are aware of

What is autonomic efferent

Involuntary muscle control

What is autonomic afferent

Sensory information we don’t know about

What is an effector

The part of the body that responds to a signal from the nervous system

How many neurons are between the brain and effector in somatic efferent division

Two

Which neurons in the somatic efferent division are myelinated

Both upper and lower motor neurons are myelinated in sometic efferent division

What neurotransmitter is used in somatic efferent division

Acetylcholine (Ach)

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What are the effectors in the somatic efferent division

Skeletal muscle

Is the somatic efferent division under voluntary or involuntary control

Voluntary control

Is the autonomic efferent division under voluntary or involuntary control

Involuntary control

Two divisions of autonomic efferent division

Sympathetic and parasympathetic

Autonomic efferent effectors

Smooth muscle, cardiac muscle, glands, fat tissue

What are preganglionic neurons

* Neurons located in the CNS (brainstem or spinal cord)
* Part of autonomic efferent division
* Extend their axons to the autonomic ganglia
* Neuron #2 in autonomic efferent division

What are postganglionic neurons

* Located in autonomic ganglia (PNS)
* Part of autonomic efferent division
* Extend their axons to the effectors
* Neuron #3 in autonomic efferent division

What are autonomic ganglia

* An area of a cluster of nerve cell bodies located outside the CNS and their activiation leads to either the sympathetic or parasympathetic response in target tissues

Which neurons in the autonomic efferent division are myelinated

Neuron #2 is myelinated and neuron #3 is unmyelinated

Which neurotransmitter does neuron #2 of the autonomic efferent division use

Acetylcholine

Which neurotransmitter does neuron #3 of the autonomic efferent division use

* Acetylcholine for parasympathetic
* Norephinephrine for sympathetic

Characteristics and effects of sympathetic nervous system

* Prepares the body for stress responses
* Fight or flight system
* Effects:
* increased heart rate
* increased blood flow to muscles, decreased blood flow to skin
* decreased gastric motility
* decreased salivation
* increased pupil size
* increased sweating

Characteristics and effects of parasympathetic nervous system

* Prepares the body for restful situations
* Rest and digest sytem
* Effects:
* decreased heart rate
* increased gastric motility
* increased salivation
* decreased pupil size

Structural differences between sympathetic and parasympathetic nervous system

Sympathetic nervous system:

* Neruon 2 has a short axon
* Neuron 3 has a long axon
* Sympathetic ganglion close to CNS

Parasympathetic nervous system:

* Neruon 2 has a long axon
* Neuron 3 has a short axon
* Parasympathetic ganglion far from CNS

What is sympathetic chain ganglia

A type of autonomic ganglia that are related to the sympathetic nervous system that are located on either side of the spinal column

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For the sympathetic nervous system, neuron #2 (preganglionic) synapses onto neuron #3 (postganglionic) in the sympathetic chain ganglia

Basic process of chemically ion gated channels

The chemical (in this case the neurotransmitter eg ACh) binds to a site on the channel, opening the channel and allowing ions to to cross the membrane, driven by the gradient.

Basic process of voltage gated ion channels

They are opened by a change in voltage, then go into an inactivated state so cannot open again until the membrane has been repolarised

Basic process of mechanically gated ion channels

Channels are gated in response to physical touch/mechanical pressure

What ion channels are on the dendrites of neurons

Chemically gated

What ion channels are on the axons of neurons

Voltage gated Na+ channels, voltage gated K+ channels, and voltage gated Ca2+ channels

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Types of ion channels

Chemically gated, voltage gated, mechanically gated

What ion channels are in dendrites and cell body

Chemically gated

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What ion channels are in axon terminals

Voltage gated Ca2+

What is presynaptic nerve terminal

The part of the axon terminal that forms a synapse with a target cell

What is a synaptic cleft

The small gap between the presynaptic and post synaptic neurons where a synapse occurs

What are synaptic vesicles

Vesicles made of membrane that are filled with a chemicall signalling substance specific to the type of nerve terminal they are in. They live in the presynaptic nerve terminal

Explain the process of a synapse

* A wave of depolarisation from the action potential along the axon reaches the terminal
* The inside of the terminal becomes positive relative to the outside
* The change in voltage activates the Ca2+ ion channelsm causing Ca2+ ions to enter the axon terminal, further increasing the positivity of the terminal
* This triggers the synaptic vesicles containing the neurotransmitter (e.g. ACh) to leave through exocytosis
* The neurotransmitter binds to the chemically gated Na+ channels, causing sodium ions to enter the postsynaptic neuron, causing a graded depolarisation
* If the depolarisation is big enough it will trigger an action potential if the threshold is reached
* The neurotransmitter is then broken down, (e.g. ACh is broken down into acetate (A) and choline (Ch) by AChE (acetylcholinesterase))
* The axon terminal reabsorbs the broken down neurotransmitter to recycle it and synthesise new molecules of ti (e.g. Ch is reabsorbed to make more ACh)

What are electrical synapses

A special type of synapse where the pre and post synaptic neuron are joined by a gap junction. Depolarisation can pass straight through this junction, meaning there is no opportunity for signal modulation which is why this type of synapse is rare

Nerve to nerve synapse information

* Synapses are tiny and there are thousands of them at each cell
* An AP in an individual neuron will rarely bring the next one to threshold
* Inputs may be exitatory or inhibitory and many neurotransmitters are used

Nerve to skeletal muscle synapse information

* Synapses are huge, each muscle fibre recieves input from only one neuron at one site
* An AP in a neuron is very likely to bring a muscle cell to threshold
* There are only excitatory inputs and only ACh is used as a neurotransmitter

What are local potentials

A localised change in voltage across the membrane of a cell which can lead to an action potential

What are inhibitory potentials

Make the membrane potential more negative (K+ ions exit)

What are excitatory potentials

Make the membrane potential more positive (Na+ ions enter)

How do local potentials turn into action potentials

Local potentials are graded (meaning the magnitude of the voltage is related to the strength of the stimulus), local potentials also undergo spacial and temporal summation (meaning the local potentials are summed over time and space). If the net voltage change of the summed local potentials exceeds the threshold an action potential will be generated

What is the usual threshold voltage for an AP

10mV

What happens at each number

(1) A graded depolarisation brings an area of excitable membrane to threshold

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(2) Voltage gated sodium channels open and sodium ions move into the cell. The membrane potential rises to \~+30mV

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(3) Sodium channels close, voltage gated potassium channels open, and potassium ions move out of the cell. Repolarisation begins

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(4) The voltage gated potassium channels begin closing. Near threshold, the voltage gated sodium channels begin reactivating, and the membrane returns to its normal resting state

What is an absolute refractory period

A period of time during the action potential where no matter how large the stimulus, another AP cannot be generated

What is a relative refractory period

A period of time during the action potential where an AP can be generated but only in response to a very large stimulus

Why are there refractory periods

To prevent the AP propogating backwards

Explain how action potentials propogate along axons

* An action potential develops at the initial segment, the membrane depolarises to +30mV
* Graded depolarisation quickly brings the membrane in segment 2 to threshold
* An AP develops in segment 2, while the initial segment begins repolarisation and is in a refractory period
* Graded depolarisation quickly brings segment 3 to threshold, while segment 2 enters a refractory period

Differences in propogation along myelinated vs unmyelinated axons

When APs are propogated along myelinated axons, the myelin acts as an insulator that the ions cant pass through so the AP ‘jumps’ from one node of ranvier to the next while in unmyelinated axons they have to travel the whole way down.

This results in myelinated axons have a much faster condunction speed than unmyelinated axons (120m/s compared to 1m/s)

Where does the spinal cord start and finish, and where is it located

Starts at the foramen magnum

Ends at 1st lumbar vertebra L1

It is located in the spinal cavity within the vertebrae surrounded by a sac of meninges

Which is the dorsal and which is the ventral side

What is spinous process

The dorsal side of vertebrae

What is conus medularis

The end of the spinal cord that is made of non neural tissue and is the attachment point for filum terminale

What is filum terminale

Fibrous, non neural tissue that anchors the spinal cord from the conus medularis to the end of the spinal cavity

Segments of the spinal cord

31 in total

* 8 pairs of cervical spinal nerves
* 12 pairs of thoracic spinal nerves
* 5 pairs of lumbar spinal nerves
* 5 pairs of sacral spinal nerves
* 1 pair of coccygeal spinal nerves