Intro to the nervous system Flashcards
What are the divisions of the nervous system?
Central nervous system and peripheral nervous system.
Give an overview of the CNS.
- encephalon and spinal cord.
- Covered with a system of membranes (meninges).
- Suspended in the cerebrospinal fluid (CSF).
List the four parts of the central nervous system.
1) Spinal cord.
2) Brain stem (nuclei of all but the first two cranial nerves), also including the medulla, pons and midbrain.
3) Cerebellum.
4) Cerebrum, consisting of;
- Telencephalon (Cerebral hemispheres).
- Diancephalon (involved in the four F’s).
What makes up the PNS?
Cranial and spinal nerves and their ganglia.
What makes up the encephalon?
Brain stem, Cerebellum and Cerebrum.
What are neurons?
Excitable nerve cells which transmit information as electric signals or “action potentials”.
Describe the structure of a typical neuron.
A typical neuron has a cell body (soma) and neurites(s). Neurite is either a dendrite or and axon.
What is an axon?
Is a single extension, can be as long as 1M, usually covered with myelin or Schwann sheath
What is a dendrite?
Are multiple, thin, short extensions.
What are neuroglia?
Specialised cells which support neurons. (more neuroglia than neurons).
What is the function of satellite cells?
Support cell soma (to support neurons).
What is the function of Schwann cells?
Myelin production in PNS (Myelin helps speed up the impulse down a neuron).
What is the function of oligodendrocytes?
Myelin production in CNS (Same as the Schwann cell).
What is the function of the Astrocytes?
Important in maintaining the blood brain barrier.
What is the function of the microglia?
They are scavengers that float around the nervous system and scrounge up remnants and scraps etc.
What is the function of the Ependymal cells?
Cerebro-spinal fluid production.
What is the difference between the glial cells and the neurons they support?
They can regenerate quite well but the neurons cannot.
What are the properties of Myelin?
- Insulation material.
- Rich in lipid and protein.
- Makes conduction faster, requiring less energy.
What are the nodes of ranvier?
Nodes of Ranvier are gaps in the myelin sheath coating on the neural axon. The nodes of Ranvier allow for ions to diffuse in and out of the neuron, propagating the electrical signal down the axon.
describe the structure of the Myelin sheath in the peripheral nervous system.
Schwann cell envelops the axon and wraps the myelin sheath around it.
Describe the structure of the myelin sheath in the central nervous system.
Oligodendrocytes can myelenate multiple neurons and can also support un-myelenated neurons.
Describe how neuronal communication works.
- Neurons communicate via synapses.
- Communication occurs between axons and dendrites.
- Vesicles full of neurotransmitters are released over the gap between the axon and the dendrite (synapse) and bind to receptors in the dendrite.
What is a ganglion?
A collection of nerve cell bodies outside the CNS
Describe the difference between the preganglionic and post-ganglionic fibres.
Pre; Thin myelinated axons from the brain stem or spinal cord.
Post; Unmyelinated axons supplying smooth muscle and glands. (They are also more numerous than the preganglionic fibres).
What is the difference between the neurons in autonomic ganglions compared to those in sensory ganglions.
Neurons in autonomic ganglions have dendrites, where as those in sensory ganglions are unipolar, having only an axon.
What are ganglions known as when they are found in the CNS?
They are known as a nucleus in the CNS.
What is the two gross appearances of the nervous system?
Grey matter and white matter.
What primarily makes up Grey matter?
Predominantly cell bodies of neurons, neuroglia and un-myelinated neurites.
Where is grey matter found?
Grey matter is on the surface of the cerebral and cerebellar hemispheres as well as in the depths of the cerebrum.
What is white matter made out of?
Axons (usually myelinated).
Where is white matter usually found?
In the spinal cord, white matter is on the surface, surrounding the grey matter and in the deeper tissues of the brain.
What imaging technique is used to generate a 3D model of the axons in the brain?
Diffusion tensor imaging (MRI).
What does the (efferent) Somatic nervous system involve?
- Innervation of the skeletal muscles.
- Voluntary
What does the (efferent) autonomic/visceral nervous system involve?
- Innervation of the cardiac and smooth muscles, glands.
- Important for internal homeostasis.
- Involuntary
What is afferent?
The input (world AFFECTS you)
What is efferent?
The output (you EFFECT the world).
What is the two divisions of the autonomic nervous sytem?
Sympathetic (Thoracolumbar),
Parasympathetic (Crainiosacral)
Describe the (autonomic) sympathetic system.
- Fight or flight
- Cell bodies are at lateral horn of T1-L2 spinal cord segments.
Describe the (autonomic) parasympathetic system.
- Rest and digest.
- Cell bodies are at brain stem or S2-4 spinal cord segments.
How many pairs of cranial nerves are there?
Twelve pairs.
What is the cauda equina?
Roots of lumbar, and lower, spinal nerves.
How is the spinal cord divided into segments?
The segments are associated with one pair of spinal nerves
What are the names of the segments of the spinal cord and the number of nerves in each?
- Cervical 8
- Thoracic 12
- Lumbar 5
- Sacral 5
- Coccygeal 1
Describe the distribution of grey matter in the spinal cord.
Grey matter is H-shaped and contains neuronal cell bodies in ‘horns’.
Describe the distribution of white matter in the spinal cord.
White matter is columns containing a number of ascending and descending tracts, all tracts are paired and most are intersected (X-shape).
What are the names of the horns of cell bodies in the grey matter of the spinal cord?
- Dorsal/posterior; Interneurons.
- Lateral horns; Visceral (autonomic) motor neurons.
- Ventral/Anterior horns; Somatic motor neurons.
What are the names of the columns in the white matter of the spinal cord?
- Ventral (anterior) columns.
- Lateral columns.
- Dorsal (posterior) columns.
What are the three components of the spinal cord?
Grey matter, White matter and the central canal.
What is different about the way cross-sections of the spinal cord is viewed compared to other tissues?
Anterior down view.
What are the external features of the spinal cord?
- Cervical and lumbosacral enlargements (areas involved in innervation of the limbs).
- Conus medullaris (end of spinal cord).
- Posterior median sulcus.
- Anterior median fissure.
Describe the spinal cord.
- A two-way impulse conduction pathways and reflex centre.
- Portected by vertebrae, meninges and CSF.
- Extends from skull base (foramen magnum) to the level of L1/L2 intervertebral disc or mid L2 vertebra
What doesn’t the spinal cord do?
Does not extnd the length of the vertebral column.
Describe the structure of the Cerebellum.
- Two hemispheres in cerebellar fossa.
- Convoluted with internal grey matter nuclei, surrounded by white matter with and outer cortex of grey matter.
- Connected to the brain stem by cerebellar peduncles (superior, middle and inferior).
What does the cerebellum do?
Processes and interprets impulses from motor cortex and sensory pathways and coordinates motor activity for smooth, well-timed movements (important for balance).
