Week 8: Organisation of the Central Nervous System Flashcards
What comprises the nervous system?
The nervous system consists of the brain, spinal cord, nerves and ganglia.
It uses nerve impulses (action potentials)
What is the nervous system responsible for?
Responsible for homeostasis, movement, sensations and special senses.
How can the nervous system be divided?
Anatomically (CNS vs. PNS), and functionally (somatic, autonomic, enteric) (sensory, motor, integrated) (voluntary, involuntary)
How can the nervous system be divided anatomically?
Central nervous system: brain, spinal cord
Peripheral nervous system: nerves, ganglia, nerve endings
What makes up the central nervous system?
The brain and spinal cord
What makes up the peripheral nervous system?
Nerves, ganglia, nerve endings
(everything other than the brain and spinal cord)
How can the nervous system be divided functionally?
Functional divisions overlap (involve both the CNS and PNS).
Somatic, autonomic, enteric
Sensory, motor, integrated
Voluntary control, involuntary control
Voluntary vs. involuntary control of the nervous system
Voluntary (conscious) control: this includes the somatic nervous system (SNS). Special senses are part of voluntary control: vision, hearing, taste, smell and touch. Motor pathways are used.
Involuntary (unconscious) control): this includes the autonomic nervous system (ANS) and the enteric nervous system (ENS). The ANS is concerned with the innervation of involuntary structures to maintain homeostasis, e.g., cardiovascular and respiratory systems. The ENS is concerned with involuntary nervous system of digestive tract. It controls digestion, movement of contents, working with the ANS.
Describe motor and sensory functional divisions of the nervous system.
Motor (efferent): CNS –> PNS effectors (skeletal, smooth, cardiac muscle, glands)
Sensory (afferent): PNS nerve endings (sensory receptors) –> CNS. PNS nerve endings are found in eyes, ears, mouth, nose, skin, joints (somatic) and blood vessels, heart, intestinal wall (autonomic and enteric)
What is meant by the integrative nervous system?
Integration of sensory and motor information in the CNS.
Nerve cells are called interneurons.
I’ve just seen my partner and can smell my dogs across the street, and after 7 years, I still get heart palpitations and run across the road to them. What divisions of the nervous system are at play?
Somatic and sensory system are involved in being able to see them across the street, and smell the dogs.
Autonomic nervous system is involved with heart palpitations
The motor nervous system is involved with running across the road.
Describe the composition of nervous tissue.
Neurons: about 10%. These send signals (action potentials), and generally cannot divide
Glial cells: about 90%. These support, segregate and insulate neurons. They retain the ability to divide, and have different types, unique to the CNS or PNS. CNS: astrocytes, oligodendrocytes, microglia, ependymal cells. PNS: schwann cells, satallite cells
Describe the structure and function of a neuron.
Dendrites: receive neural stimuli from other neurons. These can have excitatory/ inhibitory activation
Cell body: houses the nucleus and organelles. Metabolic centre which receives and processes stimuli. No mitosis.
Axon hillock: if stimuli causes depolarisation here, then action potential is initiated
Axons: conducts nerve impulse to axon terminals to effector organ/ next neuron. One per neuron. myelinated or unmyelinated.
Axon terminal: nerve impulse triggers release of neurotransmitters at synapse to communicate with other neurons/ cells
Myelin sheath: insulates the axon, increases speed of action potential conductance. Provided by schwann cells (PNS) or oligodendrocytes (CNS).
Nodes of ranvier: unmyelinated segments of axon between myelin. Impulses ‘jumps’ along these down the axon
Is a neuron and a nerve the same thing?
No - a neuron refers to the individaul cell, whereas a nerve refers to a bundle of axons.
What is a synapse?
A synapse is a specialised junction between two neurons, or between a neuron-effector cell.
1 way transmission: nerve impulse arrives at terminal, stimulates neurotransmitter release (e.g., ACh), neurotransmitter binding to receptor initiates, depolarisation in next neuron.
Give examples of neuron classification types.
Multipolar, bipolar, unipolar, pseudounipolar
Describe unipolar neurons.
Cell body has a single projection; which then divides after a short distance: one proceeds to peripheral structure, one enters the CNS.
Enables maintenance of long axons, i.e., sensory neurons
Describe bipolar neurons. Where are they found?
Bipolar = two major processes: one main dendrite and one main axon.
Rare and found in eye retina, inner ear, olfactory epithelium (in specialised functions)
Describe multipolar neurons. Give examples.
Many dendrites surrounding cell body, with one main axon.
Most common.
E.g., motor neuron (carries information from the CNS to the effector organ/ tissues), interneuron (integrates information within the CNS)
What type of neurons (structurally) have I used to see my partner?
bipolar neuron (retina of eye –> specialised function)
What type of neurons (structurally) have I used to run my dogs?
multipolar (motor system - activates muscle)
What type of neurons (structurally) have I sued to run my dogs without running into cars?
unipolar/ pseudounipolar: informationhas to be fed in by sensory system
What is glia?
- Composes 90% of nervous tissue
- Support, segregate and insulate neurons
- Types unique to CNS or PNS
What glial cells are unique to CNS?
- ependymal cells
- microglia
- oligodendrocytes
- astrocytes
Describe ependymal cells.
Forms the ependyma (thin epithelial lining of the CNS cavities called ventricles).
Simple columnar epithelium with cilia.
Produces cerebrospinal fluid (CSF)
Describe microglia cells.
- Found in the brain
- Phagocytic cells: clean up cellular debris, pathogens via phagocytosis
- Continuously survey CNS environment (if insult is detected, transforms into phagocytic microglia)
- Modulates inflammatory mediators (e.g., cytokines)
Describe oligodendrocytes.
Provides myelin in CNS
- Haphazard method of myelination
- 1 oligodendrocyte can myelinate several axons
- Unmyelinated axons are not accompanied by oligodendrocytes
Pattern of myelination is different in PNS
Describe astrocytes.
- Star shaped cells
- Numerous cellular processes
- Provide structural support (repair assistance: damage neurons degenerate, replaced by astrocytes ‘scar’)
- Homeostasis (ion and neurotransmitter regulation)
- Blood-brain barrier (BBB)
Describe the blood-brain barrier.
CNS is highly regulated as nerve cells have specific needs; must be isolated from the fluctuations in blood.
Astrocytes maintain the blood-brain barrier (BBB). All substances must pass through endothelial cell (of capillaries) and astrocytes to reach a neuron.
Substances that pass through BBB easily include glucose (no storage in brain, low blood glucose causes mental confusion, dizziness), lipid soluble substances (oxygen, carbon dioxide, alcohol, anaesthetic agents).
Substances that are blocked include; proteins, most antibiotics, many drugs (implications in drug design)
What can happen if either neurons or glia are impaired in the CNS?
Neurons and glia work together in the CNS, so if either is impaired, disease/ disorders can result:
- Uncontrolled cell division = brain tumour
- Poor myelin production/ myelin degeneration = multiple sclerosis
- Astrocytic swelling = oedema
- Neuronal cell death = stroke, trauma
- Neuronal degeneration = parkinson’s disease, alzheimer’s, motor neuron disease
How would you classify this neuron structurally? Provide an example of where you would find it.
Pseudounipolar/ unipolar
Found in sensory system
In this neuron, what organelles would you expect to find in abundance?
This neuron uses abundant ATP, so mitochondria is found in abundance.
To produce lots of proteins, needs lots of: Golgi apparatus, ribosomes, endoplasmic reticulum
This white blood cell in the blood becomes a glial cell in the brain - what is the name of that glial cell?
Microglia (in brain)
How is the surface area of the cerebral cortex/ cerebrum increased?
Gyri = ridges/ folds on cerebrum surface
Sulci - grooves between gyri
Made up of 4 lobes
What is found on the inferior surface of the brain?
12 pairs of cranial (peripheral) nerves that innervate face, mouth, eyes, ears and nose
What are the lobes of the cerebrum/ cerebral cortex? What are they involved with?
4 lobes:
1. frontal: motor (coordination)
2. parietal: sensation
3. temporal: hearing, memory
4. occipital: vision
Describe the macroscopic appearance of the brain.
Meninges - protective coverings of the brain: dura mater (outer), arachnoid mater (middle), pia mater: inner most layer.
Ventricles - cavities in the brain filled with cerebrospinal fluid (CSF)
CSF continuously produced: circulates in ventricles and subarachnoid space, surrounds and cushions brain, provides optimal chemical environment for neural activity
How can meningitis be explained?
Meningitis: inflammation of one of the layers in the meninges
dura mater, arachnoid matter or pia mater
Describe the microscopic appearance of the brain .
Consists of neurons (cell body, dendrites and axons) and neuroglia.
Grey matter: mainly neuron cell bodies (+ neuroglia, few axons) –> outside (generally)
White matter: mainly axons (+ neuroglia) –> inside (generally)
Which of the following is most tightly attached to the periosteum of the skull and the spinal column?
A. Arachnoid mater
B. Dura Mater
C. Pia Mater
D. Grey Mater
B. Dura matter
outermost later
Which mater is region X - grey or white? What will you predominantly find in this region microscopically?
Grey matter
Mainly neuron cell bodies
Describe the macroscopic appearance of the spinal cord.
Protected by the meninges just like brain (dura, arachnoid, pia mater)
Describe the microscopic appearance of the spinal cord.
Consists of neurons (cell body, dendrites and axons) and neuroglia
Describe the function of sensory receptors in the spinal cord.
Various types depending on sensation: pain, touch, pressure.
Different morphologies: free ending fibres, modified nerve endings that form specific structures
Nociceptors: specialised transducers that detect tissue damage: fast pain (A delta - myelinated axons), slow pain (C - unmyelinted axons)
Describe the function of ganglion in the spinal cord.
Sensory/ dorsal root/ spinal ganglia
- nerve cell bodies of sensory neurons reside together
- unipolar neurons
- cell body surrounded by satellite cells (PNS support cells)
- cell body maintains axon from peripheral sensory ending to synapse with interneuron/ motor neuron in spinal cord
What is the direction of information movement in the spinal cord?
Cell bodies of sensory neurons are in the dorsal root ganglia.
Sensory information enters via dorsal root of spinal nerve.
Cell bodies of motor neurons are in the ventral horn.
Motor information leaves via ventral root.
Motor information leaves via the ___ horn of the spinal cord. Which letter indicates this horn?
Ventral
D
A peripheral nerve would contain what type of fibres?
A. Sensory
B. Motor
C. Both
D. None
C. both
