Nervous System Flashcards
Describe the structure of the peripheral NS
- 12 pairs of cranial nerves
- 13 spinal nerves
- ganglion
Define a ganglion
a knot-like swelling in a nerve where neurone cell bodies are concentrated
What makes up the central nervous system ?
brain & spinal cord
What are the 2 types of cells in the nervous system ?
- neurons
- supporting cells
What makes up the autonomic division of the peripheral NS?
- Sympathetic & parasympathetic
Describe a neuron
- functional unit of the NS
- properties = excitability, conductivity & secretions
Describe the cell body of nervous tissue
- contains a nucleus surrounded by cytoplasm
- contains typical cellular organelles
What are neurofibrils ?
- composed of bundles of intermediate filaments
- provides the cell shape & support
- also made up one microtubules which asset in moving material between the cell body & axon
Describe Lipofuscin
a pigment that occurs as clumps of yellowish brown granules in the cytoplasm
What are Nissl Bodies ?
free ribosomes and prominent closures of RER in the neuronal cell bodies
What are the variations of neuron structure ?
- multipolar
- unipolar
- bipolar
- anaxonic
What are the 3 functional classes of neurones ?
- sensory (PNS)
- motor (PNS)
- interneurons (CNS)
What are the supportive cells in the nervous system ?
- astrocytes
- oligodendrocytes-myelin (CNS)
- Ependymal cells
- microglial cells
- Schwann & Satellite cells (only PNS)
What are the 2 types of astrocytes ?
protoplasmic & fibrous
Define protoplasmic astrocytes
have many short branching processes and are found in grey matter
Describe fibrous astrocytes
they have many long unbranched processes and are located mainly in the white matter
Describe astrocytes
- contain microfilaments that give them considerable strength, allowing them to support neurons
- regulates the extracellular space & ion conc.
- may play a role in learning and memory by influence the formation of neural synapses
Describe microglia
- function as phagocytes - removes microbes & damaged nervous tissue
- they remove cellular debris formed during normal development of the NS
- 10% of total brain cell population
Describe oligodendrocytes
- looks similar to astrocytes due to their projections
- involved in forming & maintain the myelin sheath around CNS axons
- a single oligodendrocyte myelinates several axons
Describe Ependymal cells
- these cells line the ventricles of the brain & central canal of the spinal cord
- cuboidal to columnar cells arranged in a single layer that possess microvilli and cilia
- produce & assist in the circulation of cerebrospinal fluid
Describe Schwann Cells
- they encircle the PNS axons, form the myelin sheath around the axons
- 1 Schwann cells myelinates 1 axon
- participates in axon regeneration
Describe satellite cells
- flat cells that surround the cell Bodie of neurons of PNS ganglia
- provides structural support
- regulates the exchanges of materials between neuronal cells bodies and interstitial fluid
What are the gaps in the myelin sheath called ?
nodes of ranvier
Define graded potentials
used for short distance communication only
What are the steps in sensory transduction ?
- stimulus
- receptor
- change in ionic permeability or afferent nerve
- generation of action potential
- propagation of action potential
- integration of information by CNS
Define action potentials
allows communication over long distance within the body
What is the electrical potential difference termed ?
resting membrane potential
Describe Ion channels
- allows the diffusion of ions like K+ & Na+
- some ion channel are gated = they only allow flow following certain stimuli
- maintains the resting membrane potential of the cell
Describe a ligand-gated channel
Opens & closes in repose to a specific chemical stimulus, such as acetylcholine/neurotransmitters/hormones
Describe a mechanically gated channel
It opens/closed in response to mechanical stimulation in the form of vibration, touch, pressure or tissue stretching
- the force distorts the channel from its resting position, opening the gate
Describe a voltage-gated channel
Opens in response to a change in membrane potential
- voltage-gated channels participate in the generation & conduction of action potentials
Why does the resting membrane potential exist ?
because of a small build-up of negative ions in the cytosol along the inside of the membrane, and an equal build-up of positive ions in the extracellular fluid on the outside surface of the membrane
The resting membrane potential arises from what 3 major factors ?
- unequal distribution of ions in the ECF & cytosol
- inability of most anions to leave the cell
- electrogenic nature of the Na/K ATPases
Describe the unequal distribution of ions in the ECF & cytosol
- extracellular fluid is rich in Na+ and chloride ions (Cl-)
- in cytosol the main cation is K+ and the 2 dominant anions are phosphates attached to molecules, such as 3 phosphates in ATP, and amino acids in proteins
Describe the inability of most anions to leave the cell
- most anions inside the cell are not free to leave
- they cannot flow the K+ out of the cell because they’re attached to non-diffusible molecules such as ATP & large proteins
Describe the electrogenic nature of the Na/K ATPases
- small inward leak of Na+ and outward leak of K+ is offset by the Na+/K+ ATPases (sodium-potassium pumps)
- these pumps remove more positive charges from the cell than they bring it
- they are electrogenic = they contribute to the negativity of the resting membrane potential
Describe a graded potential
- small devotion from the membrane potential that makes the membrane either more polarised or less polarised
Define hyperpolarising graded potential
- when a response makes the membrane more polarised (inside is more negative)
Define a depolarising graded potential
when a repose makes the membrane less polarised (inside is less negative)
When do graded potentials occur ?
when a stimulus causes mechanically gated or ligand-gated channels to open or close in an excitable cell’s plasma membrane
What does the amplitude of a graded potential depend on?
- stimulus strength
- the greater the stimuli strength, the larger the amplitude of the graded potential
Define an action potential
A sequence of rapidly occurring events that decrease and reverse the membrane potential and then eventually restored it to the resting state
What are the 2 main phases of an action potential ?
- depolarising
- depolarising
What occurs in the depolarising phase ?
- when the membrane potential of axon reaches threshold, the Na+ channel activation gates open
- As Na+ ions move through these changes into the neuron, a build up of positive charges form along inside surface of membrane and the membrane becomes depolarised
What occurs during the repolarisation phase ?
- Na+ channel inactivation gates close and the K+ channels open
- the membrane starts to become repolarised as some K+ ions leave the neuron and a few negative charges begin to build-up along the inside surface of the membrane
- K+ outflow continues, more negative charge builds along the inside surface of the membrane
- K+ outflow eventually restores the resting potential
- Na+ channel inactivation gates open
- returns to resting state when K+ gates close
What occurs during the resting state ?
- all voltage-gated Na+ and K+ channels are closed
- the axon plasma membrane is at resting membrane potential
- small build-up of negative charges along the inside surface of the membrane, and an equal build-up of positive charges along the outside surface of the membrane
Define Propagation
- conduction of action potentials across larger distances in the body
Describe what occurs at a chemical synapse
- nerve impulse arrives at a synaptic end build of a presynaptic axon
- depolarising phase opens voltage-gated Ca2+ channels
- Ca2+ flows inward through the opened channels
- increase in Ca2+ inside presynaptic neuron triggers exocytosis of the vesicles
- neurotransmitters diffuse across cleft & bind to receptors on postsynaptic neuron plasma membrane
- binding triggers opening of ligand-gated channels
- ions flow through opened channels chaining the voltage –> post synaptic potential
Describe a excitatory postsynaptic potential
- a neurotransmitter that depolarises the post synaptic membrane is excitatory as it brings the membrane closer to threshold
Describe an inhibitory postsynaptic potential
a neurotransmitter that causes hyper polarisation is inhibitory
- generation of action potential is more difficult as the membrane potential is more negative and thus even further from threshold
What are the 3 layers of the meninges ?
Dura mater, arachnoid & pia mater
What are the 5 lobes of the cerebellum ?
frontal, insula, parietal, occipital, temporal
What are the key functions of the frontal lobe ?
- abstract thought
- mood
- explicit memory
- decision making
What are the key features of the insular lobe ?
- taste
- pain
- visceral sensation
- consciousness
What are the key functions of the parietal lobe?
- somatic sensation
- sensory integration
- language processing
What are the key functions of the Occipital lobe ?
visual awareness & processing
What are the key functions of the temporal lobe ?
- hearing
- smell
- emotion
- learning
- verbal memory
What is the homunculus ?
a cortical homunculus is a distorted representation of the human body, based on the neurological ‘map’ of areas and proportions of the brain dedicated to processing motor functions and/or sensory functions
Left hemisphere functions
- specialised for spoken & written language
- sequential & analytical reasoning
- breaks info into fragments & analyses
Right hemisphere functions
- perceives information in a more integrated way
- seat of imagination & insight
- musical & artistic skill
- comparison of sights, sounds, smells and tastes
What are the functions of the spinal cord ?
conduction, neural integration, locomotion, reflexes
Describe the role of the cerebellum in motor control
- maintains muscel tone & posture
- coordinates eye & body movements
- coordinates motions of different joints with each other
- aids in learning motor skills
- lesions on the cerebellum can cause ataxia (clumsy gait)
