The Nervous System- Theme 6

What are microglia?

Small slender cells with numerous cytoplasmic processes, which have fine branches.

Do neurons have capacity for cell division?

Almost no capacity (as they are highly differentiated cells)

What does a spinal nerve divide into?

An anterior branch and a posterior branch.

What parts of the neurons are astrocytes in contact with?

Cell bodies and the axon.

In neuroanatomy what is posterior referred to? (back of the body)

Dorsal

What are cell bodies present in the peripheral nervous system organised into?

Ganglia

What are sensory axons organised into?

Ganglia

What are oligodendrocytes?

Glial cells which produce myelin and come into contact with axons.

What are somatic nerves?

Involved in voluntary functions Supply the body wall Skeletal muscle and skin contain both motor and sensory fibres.

What are astrocytes?

The largest and most numerous of the glial cell types. Their processes are in contact with the neurons and the walls of capillaries.

What is the function of astrocytes in the CNS?

Maintain blood brain barrier, Provide structural support, Regulate ion, nutrient and dissolved gas concentrations, Absorb and recycle neurotransmitters, Form scar tissue after injury (like satellite cells in the PNS).

What is the function of oligodendrocytes in the CNS?

Myelinate CNS axons and provide structural framework (like Schwann cells in the PNS).

What does the cell body/ soma contain?

Numerous dendrites which are highly branched.

What is the function of microglia in the CNS?

Remove cell debris, wastes and pathogens by phagocytosis.

What is the function of Schwann cells?

Responsible for myelination of peripheral axons and participate in the repair process after injury.

What are nerves of special sensation?

Sight, smell, taste, hearing and balance.

What is the structure of ependymal cells?

Simple, ciliated columnar.

When axons leave the CNS where do they go?

Supply motor fibres to muscles (both skeletal and smooth) and collect sensory information.

What are autonomic nerves?

Supply the internal organs. Supply the internal organs with motor (smooth muscle) and sensory fibres (for example you would need sensory information from your bladder to tell you when it is full and when to empty it- an autonomic function)

What do neuroglia do?

Support the neuron, regulate interstitial fluid and bring nutrients to the neural tissue.

What is the anterior branch of the spinal nerve called?

The Ventral ramus

What nervous system do all motor ganglia belong to?

The autonomic nervous system

What does the CNS consist of?

The brain and spinal cord

Define myotome

The group of muscles that a single spinal nerve root innervates.

What are most of the cell bodies contained within the CNS protected by?

The cranium and vertebral column

How many plexi does the spine have and where are they located?

5 Cervical, Brachial, Lumbar, Sacral and Coccygeal plexi.

What is a plexus?

A network of nerves.

What are the two primary divisions of the nervous system?

CNS and PNS

What spinal nerve supplies them all?

Thoracic spinal nerve

What do neurones do?

Transit electrical impulses along their cell membranes

When several axons are enclosed within the Schwann cell are they myelinated/ unmyelinated?

Unmyelinated (grey matter)

In neuroanatomy what is anterior referred to? (front of the body)

Ventral

Are all sensory ganglia outside the CNS?

Yes

Do all motor ganglia contain synapses?

Yes, they always contain synapses

What 2 types of nerves does the somatic nervous system consist of?

1) Afferent nerves (relay sensation from the body to the CNS) 2) Efferent nerves (send commands from the CNS to the body, stimulating contraction in skeletal muscles).

What four types of glial cells are found in the central nervous system?

1) Astrocytes 2) Oligodendrocytes (forms myelin) 3) Microglia 4) Ependymal cells

What are the three layers of the meninges in the brain?

1) Dura mater (the outermost layer made of fibrous, collagenous material). 2) Arachnoid mater (web like structure and the blood vessels supplying the brain are in that region) 3) Pia mater (the innermost layer)

What are the three types of intercostal muscle?

1) External intercostal muscles 2) Internal intercostal muscles 3) Innermost intercostal muscle

What are the two forms of protection of the brain and spinal cord, in addition to the support of glial cells?

1) From the bony cranium and vertebral column 2) From the meninges

What are the 5 functions of astrocytes?

1) Maintenance of the blood-brain barrier 2) Contain microfilaments which give structural strength to the central nervous system. 3) Produce scar tissue after injury. 4) Direct neuronal growth during development 5) Controlling interstitial environment, including recycling neurotransmitters.

What two cell types does neural tissue contain?

1) Neurones or nerve cells 2) Neuroglia

What are the two types of neuroglia found in the peripheral nervous system?

1) Schwann cells 2) Satellite cells

What extends from the cell body?

A long axon which terminates in one or more synaptic terminals, where the neuron comes into contact with another cell.

What is a spinal nerve?

A mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In humans there are 31 pairs of spinal nerves- one on each side of the vertebral column. These are grouped into the regions of the spine.

What % of glial cells do microglia usually make up?

About 5% of glial cells but their numbers rapidly increase if infection is present.

What is interstitial fluid?

Also called tissue fluid Main component of extracellular fluid Found in the interstices (the spaces between cells).

Define dermatome

An area of skin that a single nerve innervates.

What does the PNS consist of?

Axons, ganglia and supporting cells.

What occurs within the subarachnoid space?

Cerebrospinal fluid, which allows the brain to float inside this cranial cavity (not in contact with the bone of the skull). This offers the brain more protection.

Where do sympathetic ganglia lie?

Close to and on either side of the spinal cord in long chains.

What are autonomic ganglia?

Clusters of neuronal cell bodies and their dendrites. Autonomic ganglia contain the cell bodies of autonomic nerves.

Where does the ventral ramus go?

Communicates with the CNS via this anterior root (at this point it is only motor fibres to skeletal muscle)

What is the Arachnoid mater?

Covers the surface of the brain and deep to it lies the subarachnoid space which contains a meshwork of collagen and elastic fibres linking it to the pia mater. CSF fills this space.

What are somatic nerves and those of special senses (e.g. smell and taste) referred to if they originate from the brain?

Cranial nerves

How do oligodendrocytes come into contact with axons?

Either by wrapping them together or forming myelin to improve the conducting velocity of the axons.

What do microglia form from the same stem cells as?

Glial cells derived from mesoderm, which function as macrophages but in the CNS. Hence act as the first and main form of active immune defence in the CNS.

Where are cell bodies found in the peripheral nervous system and what are they supported by?

In ganglia and supported by satellite cells.

What is the Pia mater?

It is tightly attached to the brain by astrocytes and follows its contours.

What is the function of ependymal cells in the CNS?

Line ventricles (brain) and central canal (spinal cavity). Assist in producing, circulating and monitoring CSF.

When Schwann cells wrap around one axon is it myelinated/ unmyelinated?

Myelinated (white matter)

Where do parasympathetic ganglia lie?

Near to or within the organs they innervate.

Axons in the PNS are collected into bundles called...?

Nerves

What are the longest cells in the body?

Neurons (can reach over a metre in length).

Do sensory ganglia contain synapses?

No

Can neurons repair themselves after injury?

No, they have a limited capacity to repair themselves.

What are neuroglial cells?

Non nervous support cells, each with its own specific function.

Where do sensory axons, whether somatic or autonomic, have their cell bodies?

Outside the CNS in ganglia where there are no synapses.

What are the axons in the peripheral nervous system supported by?

Schwann cells, which either myelinate a section up to 1mm in length or form a simpler relationship where several axons are enclosed within the Schwann cell (unmyelinated nerve bundle)

What are somatic nerves and those of special senses referred to if they originate from the spinal cord?

Spinal nerves

What are Schwann cells?

Surround all axons in the peripheral nervous system.

What are Satellite cells?

Surround neuron cell bodies in autonomic ganglia. Regulate CO2, 02, nutrient, and neurotransmitter levels around neurons in the ganglia (supply nutrients to the surrounding neurones).

What is the posterior branch of the spinal nerve called?

The Dorsal ramus

What is the Dura mater?

The dura is a two layered structure with the outer layer fusing with the periosteum and lining the cranial cavity. The inner layer has several specialised folds which futher support the brain. The venous sinuses run in gaps between the two layers.

What muscles do the plexi mostly supply?

The limb muscles.

What do synapses on the dendrites allow for?

The neurones to communicate with each other.

What is the somatic nervous system?

The part of the peripheral nervous system associated with voluntary control of body movement, via skeletal muscles.

What space does CSF fill in the meninges and what layer of meninges is this below?

The subarachnoid space which is below the arachnoid mater.

What are ependymal cells?

These cells line the chambers and passageways of the CNS and are filled with cerebrospinal fluid (epithelial cells). They are involved in the production of CSF.

Why are the dorsal ramus and ventral ramus referred to as mixed nerves?

They have both somatosensory and somatomotor fibres.

How are ependymal cells different to other epithelial cells?

They have branching processes which make contact with other glial cells.