Nervous System 1 Flashcards
How many percent is the nervous system within our body?
3% (2kg)
How many cranial nerves are there?
12
How many pairs of spinal nerves do we have?
31 pairs
How many neurons do we have in the brain?
100 million
What are the 3 main functions of the nervous system?
Sensory function
Sensory receptors | Detect internal (e.g. blood acidity) & external stimuli (e.g. raindrops
on skin) | Carried to brain via spinal cord and cranial nerves
Integrative function
Integrates (i.e. processes) sensory information | Analyses & stores information |
Perception is integrative – Conscious awareness of sensory stimuli
Motor function
Occurs after integration of sensory information | Elicits a motor response to activate
effectors (e.g. muscles & glands)
What are the 2 main subdivisions of the nervous system?
The central nervous system (CNS) – Brain & spinal cord
The peripheral nervous system (PNS) – All nervous tissue outside of the CNS
What is the central nervous system?
The central nervous system (CNS) – Brain and spinal cord
Respond to stimuli
Generate nervous signals
Targets effectors via peripheral nervous system
What is the peripheral nervous system?
The peripheral nervous system (PNS) – All nervous tissue outside of the CNS
Somatic nervous system (SNS)
Autonomic nervous system (ANS)
Enteric nervous system (ENS)
The nervous system is primarily comprised of 2 types of cells. What are they?
Neurons
Neuroglia
Do neurons possess electrical excitability?
Yes
Neurons respond to a stimulus & convert it into an action potential. True or False
True
What is the cell body of a neuron?
The spherical part of the neuron which control all functions of the cell
Shares basic human cell organelles
Nucleus surrounded by a cytoplasm
Lysosomes
Mitochondria
Golgi complexes
Rough endoplasmic reticulum
What are the dendrites of a neuron?
Dendrites - Segments of the neuron that receive stimulation in order for the cell to become active
The receiving end of the neuron
Highly branched
Conduct impulses to the cell body
Contain organelles (control cell growth & produce energy)
What is the axon of a neuron?
Axon - Conduct impulses away from the cell body toward another neuron or effector cell
Axon hillock - Where the axon joins the cell body
Initial segment - Beginning of the axon
Trigger zone - Junction between the axon hillock and
the initial segment
What is the axon terminal of a neuron?
End point of the axon that conduct impulses away from the cell body toward another neuron
Where the axon divides into fine processes
Axon terminals swell into bulb-shaped
structures - Synaptic end bulbs
How are neurons classified?
according to the number of processes that extend from the cell body
Multipolar
Several dendrites & 1 axon
Brain| Spinal cord
Bipolar
1 dendrite & 1 axon
Eyes | Olfactory region
Unipolar
Dendrites with 1 axon fused together
Sensory receptors
How are neurons functionally classified?
Sensory (afferent) - Contain sensory receptors | Conveys an action potential towards CNS | Mostly unipolar
Interneurons (Associated) - Located in CNS between sensory & motor receptors | Integrate (process) sensory
information & elicit a motor response | Mostly multipolar
Motor (efferent) - Convey action potentials away from CNS towards effectors in PNS | Mostly multipolar
What are astrocytes?
Star shaped | Most numerous neuroglia
Contain microfilaments – Provide strength
Form blood brain barrier – Wrap around neurons & isolate CNS from rest of body
Secretion of chemicals associated with growth regulation
Maintain neural environment – Facilitate K
+ concentration
Influence synapse formation – Role in memory & learning
What are oligodendrocytes?
Neuroglia - Smaller with fewer processes than astrocytes
Form myelin sheath around (multiple) CNS axons
What are Microglia?
Neuroglia - Function as phagocytes
Remove cellular debris
What are Ependymal cells?
Neuroglia - Cuboidal to columnar cells with microvilli & cilia
Protect & nourishes the brain & spinal cord
Produce, monitor & assist the circulation of the cerebrospinal fluid
Help form blood-cerebrospinal fluid barrier
What are Schwann Cells?
Encircle PNS axons
Myelinate single axons
Can enclose up to 20 non-myelinated axons
What are satellite cells?
Surround neuronal cell bodies
Structural support
Regulate material exchange between
neurons & interstitial fluid
What is the myelin sheath?
Electrically insulates axons to increase the speed of nerve impulse conduction
Produced by oligodendrocytes in CNS
Produced by Schwann cells in PNS
Spiral multiple times around axons (~100 layers)
What are the nodes of ranvier?
Gaps of myelin sheath on axons
What is myelination?
1 Schwann cell wraps around 1 axon segment
between 2 nodes
Nervous impulse ‘jumps’ between nodes
What is white matter composed of?
Composed mainly of myelinated axons
What is grey matter composed of?
Contains cell bodies, dendrites &
unmyelinated axons & neuroglia
Nissl bodies provide grey colour
What does the somatic nervous system consist of?
Motor neurons that convey information from somatic
receptors in head, body wall, & limbs
Motor neurons that convey information from receptors
of the special senses (hearing, vision, taste & smell)
Sent to CNS
Motor neurons conduct impulses
to skeletal muscles only
Response is consciously controlled -
Voluntary
What does the autonomic system consist of?
Sensory neurons that convey information from
autonomic sensory receptors in visceral organs
(e.g. stomach & lungs)
Sent to CNS
Motor neurons conduct impulses
to smooth muscle, cardiac muscle
& glands
Response is unconsciously
controlled – Involuntary
Sympathetic or Parasympathetic
(fight or flight | rest & digest)
What does the enteric nervous system consist of?
100 million neurons in enteric plexuses
(bundles of nerves) spanning the length of the
gastrointestinal tract
Some communication with CNS
Sympathetic or Parasympathetic
(fight or flight | rest & digest)
Functions independently of the ANS & CNS
What are the 2 different types of stroke?
Ischaemic
Blood flow occluded due to blood clot | 85% of cases
Haemorrhagic
Weakened blood vessel supplying the brain has burst
What is the treatment for strokes?
Medication to prevent & dissolve blood clots | Lower blood pressure & cholesterol |
Surgery to remove clot
What is the recovery for a stroke?
Physical rehabilitation | Mental rehabilitation | Patients may never fully recover
What is the link to a stroke and the nervous system?
Stroke may lead to irreversible brain damage (ischaemic core)
Ischaemic stroke causes a state of excitotoxicity
Excitotoxicity is caused by oxygen deprivation (anoxia)
Anoxia causes glutamate transporters to fail in CNS
Accumulation of glutamate around neurons stimulate
the neuron to death
What is a neurotransmitter?
A substance released by a nerve that effects the function of another nerve, muscle, gland or cell
Approximately how many types of neurotransmitters are there?
There are approximately 100 different types of neurotransmitter
What are the functions of a neurotransmitter?
Open or close ion channels | Second messengers | Excitation or inhibition of impulses |
What are the 2 types of classifications of neurotransmitter?
Small molecule neurotransmitters
Acetylcholine | Amino acids | Biogenic amines | ATP | Purines | Nitric oxide
Neuropeptides
3-40 amino acids linked by peptide bonds | Enkephalins | Endorphins | Dynorphins | Substance P
What is Acetylcholine (ACh)?
Best-studied neurotransmitter
Excitatory neurotransmitter at some sites - Neuromuscular junction |
Inotropic receptors open cation (positively charged) channels
Inhibitory neurotransmitter at other sites - G-proteins that open
potassium channels | Inhibition of heart rate
What do the amino acids, Glutamate & Aspartate do?
Yield powerful excitatory effects
Half of synapses in brain communicate via glutamate
What do Gamma aminobutric acid (GABA) & Glycine do?
Inhibitory effects
GABA is most common in CNS | Glycine is most common in
spinal cord
Anxiety medication (e.g. Valium) enhance action of GABA.
What are Biogenetic amines?
Modified amino acids through removal of carboxyl group (decarboxylation)
What do Adrenaline & Noradrenaline do?
Biogenetic amine - Increase arousal | Excitatory effects throughout body | Released by adrenal gland into
blood
What is dopamine?
Biogenetic amine - Activated by emotional responses | Addictive
behaviours | Pleasurable experience
What is seratonin?
Biogenetic amine - Involved in sensory perception | Thermoregulation |
Control of mood | Appetite | Induction of sleep
Derivatives of ATP are also neurotransmitters . True or False?
True - Adenosine di-phosphate (ADP)
Adenosine mono-phosphate (AMP)
What is nitric oxide?
Neurotransmitter with widespread effects throughout the body
Catalysed by nitric oxide synthase (NOS) from arginine
NO is not synthesised & packaged into vesicles in advance (unlike other neurotransmitters)
NO is formed on demand, acts immediately & exists in circulation for ~10 seconds
What are the roles of nitric oxide?
Production of cyclic GMP (second messenger)
Role in memory & learning
Vasodilation of blood vessels
What are neuropeptides?
Neurotransmitters consisting of 3-40 amino acids linked by peptide bonds
Neuropeptides are formed in the neuron cell body, packaged in vesicles & transported to axon terminals
Several neuropeptides use the same receptors as opioid drugs (e.g. morphine & heroin), including:
Enkephalins (200 x stronger than morphine)| Endorphins | Dynorphins
The opioid peptides are the natural painkillers of the body
Acupuncture may produce analgesia (loss of pain) via
release of opioids
