Y12 The Nervous System Flashcards
What is homeostasis?
The maintenance of a constant internal environment.
- 37° temperature
- body fluid ( water)
- ion concentration
- glucose
- blood pressure
What are the steps of the feedback system?
- stimulus
- receptor
- Modulator
- effector
- Response
- Feedback
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
Thermoreceptors Chemoreceptors Pressoreceptors Nocireceptors Baroreceptors
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?
Hormones
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?
Functional
- sensory
- motor
- interneuron
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?
VIEW DIAGRAM
What is the first step of nerve impulse generational?
- Resting neuron contains POTENTIAL ENERGY. This comes from the difference between the electrical charge on the inside and outside of a neuron.
- 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