Flashcards in Y12 The Nervous System Deck (121):
What is homeostasis?
The maintenance of a constant internal environment.
- 37° temperature
- body fluid ( water)
- ion concentration
- blood pressure
What are the steps of the feedback system?
What happens in the stimulus stage of the feedback system?
A change in the environment, initiates a response.
What happens in the receptor stage of the feedback system?
Sensory cells detect the stimulus
List 5 types of sensory cell receptors
What do thermoreceptors detect?
Heat and cold. temperature change
What do osmoreceptors detect?
Detect changes in osmotic pressure ( pressure applied to solvents is osmosis?)
What do chemoreceptors detect?
Detect changes in blood oxygen and carbon dioxide
What do pressoreceptors detect?
Detect changes in blood pressure
What do baroreceptors detect?
Detect changes in blood pressure.
What do nocireceptors detect?
Respond to damaging or potentially damaging stimuli ( pain receptors)
What happens in the modulator stage of the feedback system?
The modulator is a control centre which processes the message from the receptors
What happens in the effector stage of the feedback system?
Effectors are Muscles, glands or cells which receive messages from the modulator
What happens in the response stage of the feedback system?
The appropriate response is made by the effector
What happens in the feedback stage of the feedback system?
The response changes the original stimulus.
Can either be positive feedback or negative.
If POSITIVE= process enhances stimulus
If NEGATIVE= process opposes stimulus
What is the nature of messages in the nervous system?
Electrical impulses and neurotransmitters
What is the nature of messages in the endocrine system?
How are messages transported in the nervous system?
Nerve impulses are Transported Along the membrane of neurons
How are messages transported in the endocrine system?
By the bloodstream
What cells are affected by nerve impulses in the nervous system?
muscles, gland cells (Effectors) and other neurons
What cells are affected by hormones in the endocrine system?
All body cells
What type of response occurs in the nervous system?
Usually local and specific responses
What type of response occurs in the endocrine system?
May be very general and widespread
How long does it normally take to respond to a nerve impulse?
Rapid response- within milliseconds
How long does it normally take to respond to hormones?
Slower response- from seconds to days
What is the duration of a nerve impulse response
Brief- stops quickly when the stimulus starts
How long does it take to respond to hormone
Longer lasting and may continue long after the stimulus has stopped
What are the types functional neurons?
What are sensory (receptor) neurons?
- receptor neurons
- carry messages from receptors in the sense organs or in the skin to the CNS ( brain and spinal cord)
What are motor (effector) neurons?
- effector neurons
- carry messages from the CNS to the muscles and glands ( the effectors)
What are interneuron?
- association neurons, connector neurons or relay neurons
- located in the CNS and are links between sensory and motor neurons
What are the types of structural neurons?
- Multipolar neurons
- bipolar neurons
- unipolar neurons
Describe multipolar neurons?
- one axon and multiple dendrites extending from cell body
- most common
- includes most interneurons in the brain and spine. and motor neurons that carry messages to skeletal muscles
Describe bipolar neurons?
- one axon and one dendrite
- axon and dendrite may have branches at ends
- bipolar neurons are found in eye, ear and nose.
- take impulses from receptor cells to other neurons
Describe unipolar neurons?
- one axon extension.
- body cell to one side of it
- most sensory neurons that carry messages to spinal cord are this type
What do functional neurons do?
Transmit information from the receptor to the effector to respond rapidly to stimuli with the purpose of maintaining homeostasis
Where does a nerve impulse start?
- in the dendrite
How does an impulse travel?
What is the first step of nerve impulse generational?
1. Resting neuron contains POTENTIAL ENERGY. This comes from the difference between the electrical charge on the inside and outside of a neuron.
2. Nerve impulse = ACTION POTENTIAL
A change in the EXtracellular fluid and intracellular fluid generates an impulse that propagates ( moves) along neuron.
~The nerve impulse undergoes polarisation, depolarisation, repolarisation, and hyperpolarisation~
What happens at polarisation?
there is a + EF (due to sodium) & - IF (due to large - proteins).
RESTING MEMBRANE POTENTIAL= -70mv
- potassium readily diffuses through cell membrane into EF. The Na/ K pump actively pumps potassium back into cell.
What happens at depolarisation?
there is a - EF & + IF ( charges have swapped)
- a stimulus opens some Na+ voltage gated channels and Na+ moves into cell causing cell to become positive .
- when membrane potential reaches -55mv an all or none response occurs
- all Na+ voltage channels open in that area causing an influx of Na+ = positive IF
What happens at repolarisation?
Charges return to + EF & - IF
- Na+ ions diffuse through IF causing in adjacent parts of the neuron to depolarise. Na+ also stimulates k+ voltage gate channels to open.
- k+ moves out of the cell into the EF making it more positive. Thence IF is - charged ( large - proteins) and Charges are restored
- This process of repolarisation generates ACTION POTENTIAL which stimulates the Na+ V.G channel in adjacent areas to open.
- the Na+/ K+ pump restores ionic distribution Na+ out and K+ in. While the cell segment is restoring back to polarised state. It is in REFARACTORY PERIOD. This prevents the neuron from being stimulated again and prevents the nerve impulse from travelling backwards
What happens at hyper polarisation?
- the charges is more negative than resting ( in the cell?) causing K+ V.G to close
- K+/Na+ pump is restoring the ionic distribution
- cell is in refractory period and cannot be restimulated and the nerve impulse is prevented from moving backwards
What are the 2 ways a nerve impulse travels along a neuron?
Saltatory conduction- mylinated conduction
Continuous conduction- unmylinated conduction
How does saltatory conduction occur? Process?
- nerve impulses Jump from one node to the next, allowing nerve impulses to travel much faster
-it jumps from nodes because nerve fibres are insulated from the extracellular fluids at the nodes of ranvier and ions cannot flow between the inside and outside of the cell membrane and action potential cannot form.
How does continuous conduction occur? Presses?
- Each action potential generates another action potential just in front of it, this repeats along the length of the whole membrane
- depolarisation in one area of the membrane causes a local current flow between neighbouring areas on the membrane.
What is a neuromuscular junction?
Junction between branches of a motor neuron and a muscle fibre; also called the motor end plate
What is a synapse?
- At Junction between branches of adjacent neurons there is a gap called the synapse.
- most occur between the end of branch of an axon of one neuron and dendrite or the cell body of another neuron.
Messages are passed across the synapse
How does transmission occur across a synapse?
1. Action potential causes depolarisation of axon terminal membrane, causing calcium V.G channels to open causing calcium to enter the cell.
What happens during transmission of an impulse across a synapse after the calcium has entered the cell?
2. Calcium ions bind to the synaptic vesicles which contain neurotransmitters. These vesicles move and then bind to the presynaptic membrane allowing neurotransmitters to be released via exocytosis into synaptic cleft.
What happens during impulse transmission across a synapse after neurotransmitters are be released via exocytosis into synaptic cleft.
3. Neurotransmitters diffuse across the cleft and bind to receptors.
i.e sodium ligand channels
Protein channels open causing sodium to enter the cell causing depolarisation of post synaptic membrane
4. Action potential probates through post synaptic membrane. Neurotransmitters are broken down and removed from receptor mediated proteins.
i.e Aceylcholinenesterase breaks down Acetylcholine into Acetyl CoA and chlorine. Acetyl coa and chlorine are then recycled, taken up into the cell via endocytosis and converted back into acetylcholine at the axon terminal
Describe the parietal cerebral lobe?
-It is in between the frontal and occipital lobe
- primary sensory strip and association area
- processes tactile information, pain etc.
Describe the frontal lobe?
- front of the brain
- voluntary control of muscles
- judgement, emotions, motivation and memory
- categorising, thinking and expressive language
Describe the occipital lobe?
- Helps with vision
- behind the parietal lobe
Describe the temporal lobe!
- olfactory (smelling) and auditory areas
- speech auditory processing
- processing of emotional responses
Physical features of the cerebrum?
- largest part of brain
- divided into four lobes
- cerebral cortex is its outer layer
- below cerebral cortex is white matter
- convoluted surface
Function of cerebrum?
Frontal- primary motor cortex, responsible for voluntary movement of muscles, judgement and emotions
Temporal- olfactory, auditory processing and emotional responses
Parietal- processing tactile information, pain ect. Sensory association area
Physical features of cerebral cortex?
-outer surface of cerebrum
Function of cerebral cortex?
Higher order functions such as thinking, reasoning, memory, learning and conscious awareness of surroundings
Physical features of frontal lobe?
Front of brain...
Function of frontal lobe?
-Primary motor cortex
- responsible for voluntary control of muscles
- forming strong memories, thinking, reasoning and expressive language
Physical features of the corpus callosum?
- wide band of nerve fibres that lie underneath cerebrum at the base of the longitudinal fissure
- nerve fibres cross from one cerebral hemisphere to another allowing communication between sides
Functions of corpus callosum?
Communication between two hemispheres
Physical features of the thalamus?
- dual lobed
- mass of grey matter
- beneath cerebral cortex
Functions of thalamus
- directs nerve impulses to correct parts of brain
- relate sensory motor signals to cerebral cortex
- receives auditory and visual signals
Physical features of hypothalamus?
- middle of the brain, can’t be seen from outside
Function of hypothalamus?
- involved in homeostasis
- eg, regulation of autonomic nervous system ( regulation of heart rate, blood pressure etc.)
- regulation of body temp, food and water intake, patterns of waking and sleeping and control of urinary bladder
Physical features of pituitary gland?
- middle of the base of skull
- pea sized
- below hypothalamus
Function or pituitary gland?
- secretes hormones directly into bloodstream and produces hormones for various bodily functions
Physical features of pons?
- part of brain stem
- a bulge
Functions of pons?
- message station that directs Impulses
- relays signals from forebrain to cerebellum
-has sensory soles in hearing, taste and facial sensations
Physical features of spinal cord?
- roughly cylindrical in structure
- extends from the large opening at the base of the skull to the second lumbar vertebrae
- about 44cm
- enclosed in vertebrae canal and bone
- cross section shows grey matter at center surrounded by white matter (g matter is H shape )
Function of spinal cord?
-Carry sensory impulses up to brain and motor impulses down from brain
- integrate certain reflexes (fast automatic responses)
Physical features of cerebellum!
- under rear part of cerebrum
- second largest part of brain
- surface folded into series of parallel ridges
- outer folded part is grey matter
- inside is white matter that branches to all parts of cerebellum
Functions of cerebellum?
- Control over posture, balance and coordination of voluntary muscle movement
- does this by receiving sensory information from inner ear ( for posture and balance ) and from stretch receptors in skeletal muscles
Physical features of medulla oblongata?
- continuation of spinal cord
- 3cm long
- extends from where spinal cord enters skull
- nerve fibres pass through going to and from parts of brain
Functions of medulla oblongata?
Cardiac centre- regulates the rate and force of heart rate
Respiratory centre- controls rate and depth of breathing
Vasomotor centre- regulates diameter of blood vessels
+ others they regulate reflexes of swallowing, sneezing and vomiting.
- centres are controlled by higher centres in the brain.
What type/part of neuron would Salutatory conduction occur in?
What type/part of neuron continuous conduction occur in?
Speed of Saltutory conduction?
Saltatory = 140 m/s
Speed of continuous conduction?
Continuous = 2 m/s
structural features of a sensory neurons?
- sense receptors on the end of the axons. Dendrites are attached to receptors
- axon terminals of on the opposite side of the axon
structural features of a inter neurons?
- dendrites surround cellbody
structural features of a motor neurons?
- effectors on one end and dendrites on other surrounding cell body
From the peripheral nervous system where does an impules go?
Either via the after afferent division (sensory) of the Efferent division (motor)
What is the afferent pathway?
Going towards the brain
What is the efferent pathway?
(Exiting) going away from the brain
Where do impulses of the afferent route come from?
They come from either somatic sensory neurons or visceral sensory neurons
Somatic sensory-information from skin and muscles
Visceral sensory- information from internal organs
What are the two route motor impulses may take?
Somatic- sends impulses to skin and muscles
autonomic- sends impulses to involuntary muscles, organs
Where do impulses that travel via the Autonomic nervous system division go?
Via the sympathetic route or the parasympathetic route.
Sympathetic- controls body when active; fight of flight response
Parasympathetic- controls body when resting, quiet
From the peripheral nervous system, where does an imuulse go ( when it has come from either afferent or efferent pathway)
To the CNS and back
Features of the spinal cord?
- dorsal root with ganglion ( lump)
- dorsal root (back of spine, vertebrae)
- sensory neuron
- ganglion ( cell bodies on sensory neurons)
- central canal ( inside H shaped grey matter)
- white matter ( surrounding H)
- motor neuron through ventral root
What does the spinal column contain?
- vertebrae ( bones forming the backbone)
-vertebral Canal ( fat, blood vessels, connective tissue which provide extra cushioning)
- meninges and cerebral spinal fluid
When a sensory impulse reaches grey matter in spine, how does it get up to the brain? And back.
Sensory neuron sends the impulse to an interneuron which sends the impulse to another a sensory neuron which leads it up the ascending tract to the brain. A motor neuron then brings it back down the descending tract sending the impulse to an interneuron which transmits the message to another motor neuron which takes it to the effector.
What is a mixed nerve?
a nerve containing both sensory and motor fibers
What are the protective features of the CNS?
- meninges consisting of the Dura Mater, arachnoid and Pia Mater
How does skin protect the CNS?
It is the outermost layer it acts as a barrier
How does periosteum protect the CNS?
Acts as a layer of connective tissue which surrounds bone
How does bone protect the CNS?
Brain is protected by the skull and the cranium which house it.
Vertebrae also protect spinal cord by covering it
What are the layers of the maninges?
How does the Dura Mater layer of the meninges protect the CNS?
- tough and fibrous
- sticks close to bones of skull but on inside if vertebral Canal is not so close fitting
- toughest layer
- pain sensitive
- space containing fat, connective tissue and blood vessels which serve as padding
- veins that carry blood from the brain back to heart
How does the arachnoids layer of the meninges protect the CNS?
- middle layers
- filled with web of collagen
- has cerebral fluid
- no blood vessels
- contains CSF
How does the Pia Mater layer of the meninges protect the CNS?
- sticks closely to surface of brain and spinal cord
- very tender
- rich supply of blood vessels which provide nutrients to nervous tissue
- help deliver nutrients to brain and spinal cord
What does Cerebral spinal fluid do?
-occupies space between middle and inner layer of meninges. It is formed fr9m blood and circulates around CNS eventually reentering capillaries
protection: acts as shock absorber
Support: brain floats in it
Transport: takes nutrients to brain cells and spinal cord, removing wastes
What is the general function of the autonomic division?
Adjustment of internal environment (homeostasis)
General function of the somatic division?
Response to the external environment
Effector affected in the Autonomic division?
Heart muscles, involuntary muscles and glands
Effectors affected by the somatic division?
Skeletal( voluntary) muscles
Efferent outwards pathway for the Autonomic division?
To nerve fibres from the CNS to the effector with a synapse in a ganglion
Efferent ( outward) pathway for somatic division?
One nerve fibre from the CNS to the effector; no synapse or ganglion
Autonomic division, type of neurotransmitters at effector
Acetylcholine or noradrenaline
Somatic division, type of neurotransmitters at effector
Is Autonomic division voluntary or involuntary
Is Autonomic division voluntary or involuntary?
How many nerve to get to the target organ?
Two sets- sympathetic and parasympathetic
How many nerves to get to the target organ?
What is the effect on the target organ in Autonomic division?
Excitation or inhibition
What is the effect on the target organ in Autonomic division?
What is excitation?
the process by which nerve cells use their “presynaptic terminals” to stimulate the next receiving nerve cell in line to transmit information onward.
What is inhibition?
kind of synaptic potential that makes a postsynaptic neuron less likely to generate an action potential.