HUBS191 Module 3: Nerves and Muscles (neuroanatomy and neurophysiology)

Cells and organisation of the nervous system,

Functions of the nervous system

Detects internal and external environment, integrates information in CNS, produces coordinated motor responses, maintains homeostasis

Basic organisation of the nervous system

Central nervous system (brain and spinal cord), Peripheral nervous system (nerves and ganglia)

Brain and spinal cord

Components of the central nervous system

Nerves and ganglia

Components in the peripheral nervous system

Function of brain and spinal cord

Integration and coordination

Function of nerves and ganglia

Communication between body and central nervous system

Afferent

Sensory information travels into the central nervous system

Efferent

Motor output travels out of the central nervous system

Two main cell types in the nervous system

Neurons and glial cells

Neurons

Excitable cells which generate action potentials and transmit information

Glial cells

Cells which support neurons, providing nutrients, insulation and immune defence

Structure of a neuron

Dendrites, cell body, axon hillock, axon, axon terminals

Dendrites

Branch like extensions of a neuron which receive chemical signals from other neurons and contain receptors for neurotransmitters carrying signals towards the cell body

Cell body (soma)

Contains nucleus and organelles and is the site of metabolic activity, integrates incoming signals from dendrites and sends processed signals to axon hillock

Axon hillock

Junction between soma and axon and is the summation zone which determines whether threshold is reached to initiate action potential

Axon

Long, thin projection from neuron which conducts action potentials and carries signals away from the cell body

Axon terminals

End branches of axon which contain synaptic vesicles with neurotransmitters and release neurotransmitters into synapse converting electrical signal to chemical signal

Action potential

A rapid electrical signal caused by ion movement across a membrane

Functional zones of a neuron

Input zone, summation zone, conduction zone, output zone

Multipolar neurons

Many dendrites and one axon, integrating lots of input

Bipolar neurons

One dendrite and one axon, having specialised sensory roles e.g vision

Unipolar neurons

Single process branching into two, fast signal transmission

Anaxonic neurons

No distinct axon, integrates signals locally

Main types of glial cells

Astrocytes, microglia, ependymal cells, oligodendrocytes, shwann cells

Functions of astrocytes

Provide metabolic support, surround blood vessels, maintain extracellular environment, form glial scar after injury

Functions of microglia

Immune cells of central nervous system derived from myeloid lineage that engulf pathogens and debris

Functions of ependymal cells

Line ventricles and spinal canal, contain cilia which helps circulate cerebrospinal fluid

Functions of oligodendrocytes

Form myelin sheath in central nervous system, one cell myelinates multiple axons and increases conduction velocity

Functions of schwann cells

Form myelin in peripheral nervous system, one cell wraps one axon segment and supports nerve regeneration

Myelin sheath

Lipid rich insulating layer which prevents current leakage and speeds up signal transmission

Nodes of ranvier

Gaps between myelin allowing saltatory conduction and increase speed

Structure of a synapse

Presynaptic terminal, synaptic cleft, postsynaptic membrane

Process occuring at the synapse

Action potential arrive, vesicles release neurotransmitters, neurotransmitters diffuse across cleft, bind receptors and a new signal is generated

Role of neurotransmitters

Chemical messengers, bind to receptors, trigger response in postsynaptic cell

Grey matter

Neuron cell bodies in cerebral cortex or spinal cord

White matter

Bundle of axons, long fibre tracts in cerebral cortex or spinal cord

Nucleus and tract in CNS

Nucleus- group of cell bodies
Tract- bundle of axons

Ganglion and nerve in PNS

Ganglion- group of cell bodies
Nerve- bundle of axons