Unit 2 - Nervous System Flashcards
structure & function of a neuron: cell body, dendrites, axon, myelin sheath, Schwann cell, node of ranvier, neurilemma
Cell Body - contains nucleus - responsible for controlling the functioning of the cell
Dendrites - Short extensions - carry nerve impulses into cell body
Axon - carries nerve impulses away from the cell body
Myelin sheath - insulates, protects and speeds up the movement of impulses along the axon
Schwann Cell - forms the myelin sheath only within the PNS
Node of Ranvier - facilitates the rapid transmission of nerve impulses
Neurilemma - outermost coil of Schwann cells
Neurons classified by function
sensory - carry messages from receptors in the sense organs, or in the skin, to the central nervous system
Motor - carry messages from the CNS to effectors
Interneurons - link between the sensory and motor neuron
Define nerve impulse (3)
- the message that travels along a nerve fibre
- transmission of a nerve impulse triggers an action potential in the adjacent membrane
- Impulse conducts along unmyelinated fibres through salatory conduction (jumping conduction - jumps from one NOR to another)
transmission of a nerve impulse
Polarisation
○ At a resting, potential the membrane is polarised
○ inside of the cell and has a net negative charge and the outside of the cell has a net positive charge.
○ A Na/K pump allows these ions to move across the membrane: sodium into the cell and potassium out
Depolarization
○ the sudden increase in membrane potential
- ligand-gated channels open
○ If the stimulus is strong enough to increase the potential to -55mV then voltage-gated sodium channels open
○ This produces a movement of sodium ions into the cells
○ The size of the response is not related to the strength of the stimulus, this is also known as the all or none response)
Repolarization
○ The sodium channels close, which stops the influx of sodium ions
○ At the same time, voltage-gated potassium channels open, increasing the flow of potassium ions out of the cell
○ This makes the inside of the membrane more negative than the outside and decreases the membrane potential
○ The membrane is repolarized
○ The potassium channels remain open longer than what is needed, this results in the membrane potential dropping lower than the resting membrane potential, and the membrane is hyperpolarized
○ This process is called hyperpolarization
4) Refractory Period
○ Once the sodium channels have opened they quickly become inactivated
○ Thus being unresponsive to stimulus
○ Therefore, for a brief period after being stimulated, the membrane will not undergo another action potential
Transmission across a synapse
- Nerve impulse reaches the axon terminal, it activates voltage gated calcium ion channels
- As there is a higher concentration of calcium ions in the extracellular fluid, they flow into the cell at the pre-synaptic axon terminal
- This causes synaptic vesicles to fuse with the membrane, releasing special chemicals called neurotransmitters by exocytosis
- The neurotransmitters diffuse across the gap and attach to receptors on the membrane of the next neuron
- This stimulates ligand-gated protein channels to open, which allows the influx of sodium ions an initiates an action potential
conduction along unmyelinated fibres (3)
- depolarisation of one area causes depolarisation in another area of the membrane
- this movement stimulates the opening of voltage-gated sodium channels, initiates action potential in the membrane
- refractory period prevents the impulse going backward as action potential cannot be generated
transmission along myelinated fibres
- myelinated fibres prevents the diffusion of ions through the membrane
- action potential jumps from one node to another (as it is unmyelinated)
- saltatory conduction = faster
thermoreceptors
- sensitive to heat & cold
peripheral in the skin informs the brain (hypo & cerebrum)
osmoreceptors
- in the hypo (thirst centre)
- sensitive to concentration of substances in water (osmotic pressure)
chemoreceptors
- mouth (taste) nose (odour)
peripheral (aortic & carotid bodies)
*body fluids e.g. pH, CO2, O2
central (medulla) - CO2 & pH
nociceptors
- stimulated by damages to the tissue e.g. poor blood flow, excessive stimuli such as heat
touch receptors
- surface of the skin, sensitive to touch, nerve endings & follicles
- others located deep down sensitive to vibrations & pressure
Central Nervous System Protection
Bone - cranium and vertebral canal
Meninges - duramater, arachnoidmater and pia mater
CSF - clear watery fluid
Describe the layers of the meninges
○ Dura mater - outermost layer, tough and fibrous, texture and thickness similar to rubber glove
○ Arachnoid mater - loose mesh of fibres - resembles web
Pia mater - inner layer, delicate - contains many blood vessels and sticks closely to the surface of the brain and spinal cord
What are the three main functions of the CSF
- Protection - acts as a shock absorber
- Support - brain floats inside it
- Transport - CSF is formed from the blood, and circulates around and through the CNS before eventually re-entering the blood capillaries. During its circulation it takes nutrients to cells of the brain and spinal cord
Describe the different parts of the brain - cerebrum, medulla obligate, cerebellum and corpus calloscum
Cerebrum - responsible for thinking, reasoning, learning, memory and sense of responsibility. Has a large surface area due to its folded structure.
Medulla oblongata - joins the brain to the spinal chord
Cerebellum - part of the brain behind and below the cerebrum; concerned with coordination of movement
Corpus callosum - bundle of nerve fibres that links the two cerebral hemispheres
Divisions of the PNS
Afferent( sensory)
Efferent (motor) ->1. Somatic 2. Autonomic -> Sympathetic & Parasympathetic
What is the structure and function of the autonomic and somatic nervous system
Autonomic
Structure - groups of nerve cells in the medulla oblongata, hypothalamus and cerebral cortex
Function - controls the body’s internal environment and is involved in many of the mechanisms that keep it constant
Somatic
Structure - nerves and neurons
Function - responds to the external environment
what is the structure and function of the sympathetic and parasympathetic nervous system
Parasympathetic
Function - generally produces responses that maintain the body during relatively quiet condition
Sympathetic
Function - produce responses that prepare the body for strenuous physical activity
Compare how the afferent and efferent nervous system detects and responds to changes in the internal and external environments
Afferent
- Internal
carries impulses into the CNS from receptors in the skin
- External
notifies internal of impulses
Efferent
- Internal
carries impulses away from the CNS
- External
takes impulses from the somatic and autonomic PNS
Compare how the autonomic and somatic nervous system detects and responds to changes in the internal and external environments
Autonomic
- Internal
adjustment of the internal environment - affects heart muscles, involuntary muscle, and glands
- External
No detection
Somatic
- Internal
no detection
- External
responds to the external environment - effects skeletal muscles
Compare how the sympathetic and parasympathetic nervous system detects and responds to changes in the internal and external environments
Sympathetic
- Internal
everything from above and blood vessels of skin, skeletal muscle and internal organs
- External
no detection
Parasympathetic
- Internal
Heart, lungs, stomach and intestines, liver, iris, salivary gland, and urinary bladder
- External
no detection
Q
what specific parts of the central nervous system have roles in the co-ordination of body functions and are protected by the bones of the skull, the meninges and cerebro-spinal fluid
Brain - cerebrum, cerebellum, medulla oblongata, hypothalamus, corpus callosum
Spinal cord
what specially structured neurons are in the reflex arc and are used to transmit information from the receptor to the effect
Sensory (PNS)
Interneurons (CNS)
Motor (PNS)
nervous vs endocrone
nervous
*rapid
*short lasting
*utilises electrical impulses
*influence one effector
endocrine
*slower
*long lasting
*utilises hormones
*affects number of diff organs
how does the central nervous system relay neurons
Through its interneurons, which as the same suggest connects sensory and motor neurons by going in between them.
How do osmoreceptors detect changes in the internal and external environments?
Internal - determines osmotic pressure
- determined by the concentration of substances dissolved in the water of the blood plasma
- located in the hypothalamus and are sensitive to even very small changes
How do chemoreceptors detect changes in the internal and external environments?
Internal
- sensitive to the pH of the blood and to the concentrations of oxygen and CO2
External
-Present in nose, causing smell and present in mouth causing taste
How do touch receptors detect changes in the internal and external environments?
External
- nerve endings send impulses to the brain
How do pain receptors detect changes in the internal and external environments?
External and Internal
- stimulated by damage to the tissues
- occurs everywhere but brain
How does the parasympathetic division effects its target organs
Heart - decrease rate and strength of contraction
Lungs - constricts bronchioles
Stomach, intestines - increases movement
Liver - increases uptake of glucose and synthesis of glycogen
Iris - constricts pupil
Sweat - no effect
Salivary glands - increases secretion of saliva
Blood vessels - little to no effect
Urinary bladder - constricts muscles of wall
Adrenal medulla - no effect
describe the spinal cord structure
- white matter surround the grey matter in the centre arranged in bundles called tracts
ascending tract:
*sensory axons that carry impulses towards the brain
descending
*motor axons carry impulses away from the brain
spinal cord function
- carry sensory impulses up, motor impulses down
- integrate fast automatic responses aka reflex
what is the structure and function of the central and peripheral nervous system
Central
Structure - brain and spinal chords - protected by bone, meninges and cerbrospinal fluid
Function - receives and processes incoming messages and outgoing messages are initiated
Peripheral
Structure - cranial nerves and spinal nerves
Function - takes messages from receptors to the CNS and from the CNS to muscles and glands
what is the structure and function of the afferent and efferent nervous system
Afferent
Structure - nerves and neurons
Function - carry impulses into the CNS
Efferent
Structure - nerves and neurons - carry away from the CNS - divided into somatic and autonomic
Function - carry impulses away from the CNS
What is the structure and function of the autonomic and somatic nervous system
Autonomic
Structure - groups of nerve cells in the medulla oblongata, hypothalamus and cerebral cortex
Function - controls the body’s internal environment and is involved in many of the mechanisms that keep it constant
Somatic
Structure - nerves and neurons
Function - responds to the external environment
what is the structure and function of the sympathetic and parasympathetic nervous system
Parasympathetic
Function - generally produces responses that maintain the body during relatively quiet condition
Sympathetic
Function - produce responses that prepare the body for strenuous physical activity
how does the sympathetic division effect its target organs
Heart - increases rate and strength of contraction
Lungs - dilates bronchioles
Stomach - decreases movement
Liver - increases breakdown of glycogen and release of glucose
Iris - dilates pupil
Sweat Glands - increases sweat secretion
Salivary glands - decreases secretion of saliva
skin blood vessels - constricts vessels
Skeletal muscle blood vessels - dilates
Internal organ blood vessels - constricts
Urinary bladder - relaxes muscles of wall
Adrenal medulla - stimulate hormone secretion
