Nervous System 11.1 Flashcards
Everything period.
Homeostasis
Stability within the body
What does the Human Nervous system do?
It responds to changes in body and external environment
It regulates body structures and is composed of many subsystems that work together to maintain homeostasis
It monitors and controls most body processes
What is the central Nervous System and what does it do?
It is the Brain and the Spinal cord
It processes and integrates information sent by nerves
What is the peripheral nervous system and what does it do?
Anything that is not in the centre (brain or spinal cord)
It sends sensory messages to CNS via nerves
It sends sensory information from CNS to muscles and glands
Sensory pathways?
Pathway that has nerves that carry sensory messages to the CNS
What is the motor pathway?
Pathway that has nerves that send sensory information from CNS to muscles and glands
Explain the Somatic Nervous System?
It is under conscious control - voluntary
Consists of sensory receptors in the head and extremities
Consists of nerves that send sensory information to CNS
Nerves that send instructions from CNS to skeletal muscles
Explain the Autonomic Nervous System?
Not under conscious control - involuntary
Controls glandular secretions - and the functioning of smooth and cardiac muscles
What are the categories under the Autonomic Nervous System and what do they do?
Sympathetic Nervous System and Parasympethic Nervous System
- They work in opposition to regulate the involuntary process of the body
Examples of Involuntary processes?
Breathing and heart rate.
The two main types of cells that compose the nervous system?
Neurons and glial cells
What are neurons?
They are macroscopic and the basic structural and functional units of the nervous system
Specialized the respond to physical and chemical stimuli to conduct electrochemical signals - release chemicals that regulate various body processes
What is the name of the tissue that neurons are organized into?
Nerves (covered by a connective tissue)
Where do nerves extend the neurons?
Through the peripheral nervous system.
What are glial cells?
They are a supporting framework that support neurons
They nourish the neurons, remove wastes, and defend neurons against infections
They account for half of the volume of the nervous system
What are the three main neurons that form basic-impulse pathways?
Sensory neurons, interneurons, and motor neurons
What are the three overlapping functions that make the nervous system?
Sensory Input, integration, and motor output?
Describe the sensory input.
Sensory neurons carry information from sensory receptors (senses) to CNS
Describe integration.
Found in CNS - act as a link between sensory and moto neurons -
Integrates and process incoming sensory information
Relays outgoing motor information
Describe motor output.
Motor neurons transmit information from CNS to effectors
What are reflexes?
sudden, unlearned, involuntary responses to to certain stimuli
What is a reflex arc?
a simple connection of neurons - results in reflex action in response to a stimulus
How many neurons do withdrawal reflexes use?
Depend on three neurons
Why do we not feel pain before we respond to stimuli?
The impulse is carried from the sensory neuron to interneuron in the spinal cord then to the motor neuron which instructs effectors to react
The sensory neurons do not pass the brain - There is not enough time for the brain to process this and involve itself with voluntary control
Brain processes what has happened after reflex - hence why we feel pain after
What four common features do neurons share?
Axons, dendrites, cell body (soma), and branching ends
Describe the dendrites appearance.
Highly branched, numerous, short,, branching terminals.
What benefit comes from dendrites being numerous and highly branched?
It increases the surface area to receive information
What do dendrites do?
They receive impulses from other neurons and sensory receptors - relay impulse to the cell body
Describe the appearance of the cell body?
It contains the nucleus - and is the site of the cell’s metabolic reactions
What does the cell body do?
It processes input from dendrites - if the input is large enough - relays it to the axon (where an impulse is initiated)
How long are axons?
They range in length depending on where in the body they are located (from 1mm to 1m)
What is a nerve in the body with a long length of axons?
Sciatic nerve - in leg
Contains neuronal axons that go from the spinal cord to foot (over 1m)
What do axons do?
Conduct impulses away from the cell body.
What does the terminal end of axons do?
Branches into many fibres.
What does the axon terminal do?
Releases chemical signals in the space between it and sensory receptors on other dendrites
Does this to communicate with adjacent neurons, glands, or muscles
How many axons per neuron?
One
Describe myelin sheath?
fatty, insulating layer that encloses the axons of some neurons
Gives axons white, glistening appearance
What does myelin sheath do?
It protects myelinated neurons - and speeds the rate of nerve impulse transmission!
What forms myelin?
Schwann cells
How do Schwann cells form myelin?
Schwann cells form myelin by wrapping itself around the axon.
What are myelinated neurons known as?
White matter
What are unmyelinated neurons known as?
Grey matter
Are most neurons in the PNS myelinated or not?
Mostly myelinated
Who was Luigi Galvani?
Italian physicist and anatomist - discovered the electric nature of the tissue
Two rods and a wire - made frog leg twitch
What did A.L Hodgkin perform on and why?
A squid - they have bigger axons on humans so the potential difference across membrane is easier to measure.
How is the potential difference measured?
Insert electrode in axon - read potential difference from specialized voltameter
How does nerve conduction differ from electrical conduction?
It is slower and more complex
Depends on the movement of ions across the cell membrane of the axon
When microelectrodes are inserted into an inactive/resting neuron, what do measurements on the voltameter indicate?
They indicate an electrical potential difference (voltage) across the neural membrane
Chemical reactions maintain a separation of charges between positive and negative poles. True or False?
True
What is the charge of the cytoplasmic side in a resting neuron?
Negative
What is the charge of the extracellular side in a resting neuron?
Positive
What is membrane potential?
A charge separation across the membrane, a form of potential energy
What is resting membrane potential?
Potential difference across the membrane in a resting neuron
What is the resting potential in most neurons?
-70mV (negative on inside, positive on outside)
What does resting potential do?
Provides energy for the generation of a nerve impulse - in response to appropriate stimulus
What is polarization?
Process of generating a resting membrane potential of -70mV
What is the cell membrane of the axon inpermeable to?
Large Protein molecules
Small negatively charged ions (Chloride)
* Contribute to the negative charge in cell
What is the most important contributor to the separation charge and the resulting electrical potential difference across the Membrane?
The sodium-potassium exchange pump
What is the sodium potassium exchange pump?
System involving carrier proteins in the plasma membrane - that uses the energy of ATP to:
transport sodium ions out
Transport potassium ions in (in animal cells?)
How many potassium ions would diffuse outside of the membrane?
Two
How many sodium ions would diffuse inside of the membrane?
Three
Where is the energy that the resting membrane potential generate, stored?
It is stored in the electrochemical gradient across the membrane - waiting for an impulse to occur
What does it mean by “resting” neuron?
No nerve impulses are being sent across the axon.
What do nerve impulses consist of?
A series of action potentials.
Where do action potentials occur?
At the nodes of Ranvier on myelinated neurons.
When is a neuronal membrane said to be depolarized?
If the transmembrane potential is reduced to less than -70mV.
What is the dramatic change that occurs if the membrane at the node of Ranvier becomes depolarized to -55mV?
An action potential.
Why is an axon called an all or none event?
Because depolarization to between -70mV and -55mV has no effect
It either fully responds to stimuli or doesn’t
Which depolarization measurements will produce identical action potentials?
Depolarization of -55mV or up to 0.
What is the potential of -55mV called?
Threshold potential
What happens when transmembrane potential at the nodes of Ranvier reach threshold? (Think sodium ions)
Voltage gated sodium ions open
Make it permeable to sodium
What happens as the sodium ions come rushing in to the cell during depolarization?
There is a net positive charge of +35mV.
What does the change in membrane potential cause the potassium to do?
It causes the potassium voltage gates to open
Potassium flows out
Inside of cell is left with a negative net charge of: -90mV (it is repolarized)
What brings the membrane back to resting potential (-70mV) after an action potential?
Natural diffusion and the sodium-potassium exchange pump
What is the period that happens after an action potential?
Refractory period - membrane cannot be stimulated to produce another action potential
What happens to the sodium ions when an action potential occurs and the sodium gate has been closed and there is no where to diffuse?
The sodium channel closes - high concentration of sodium ions in the cell - they diffuse in both directions along the axon
As the sodium travels down the axon what does it do?
As the reach neighboring nodes of Ranvier - positive charge reduces net negative charge in membrane - nodes of Ranvier become depolarized to threshold (creates impulse from here)
What does refractory period prevent?
It prevents the impulse from going backwards.
Why are action potentials forced to “jump” from one node of Ranvier to the next?
Because of the myelin sheath that surrounds some of the axons.
What is saltatory conduction?
The conduction of an impulse along a myelinated neuron.
What causes multiple sclerosis and how does this hurt the nervous system?
The breakdown of myelin surrounding the axons in the central nervous system
Neurons can no longer transmit electrochemical signals between the brain and body
What is autoimmune disease and what are the symptoms?
When the bodies immune system breaks down the myelin sheath
blurred vision, loss of balance, muscle weakness, fatigue, and slurred speech
What is a synapse?
Connection between two neurons - or a neuron and an effector
What is a neuromuscular conjuction?
Synapse between motor neuron and a muscle cell
What is the synaptic terminal?
It is at the end of the axon - converts electrical energy (action potentials )into chemical energy (neurotransmitters)
What is the synaptic cleft?
The gap between neurons.
Some neurons with a synaptic cleft between the two are not close enough for the impulse to jump - what do they use instead?
Neurotransmitters (chemical messengers)
What are synaptic vessicles?
Sacs that contain neurotransmitters
Release neurotransmitters into the synaptic cleft (through exocytosis)
What do the neurotransmitters bind to when they reach the postsynaptic membrane?
They bind to receptor proteins.
How long does it take the neurotransmitters to reach the postsynaptic neuron?
0.5 to 1m/s.
What do receptor proteins trigger?
They trigger ion specific channels to open - depolarizing membrane - if threshold potential is reached - action potential is initiated
What are the excitatory effects that the neurotransmitters have on the postsynaptic membrane?
Receptor proteins allow ion channels to open
Sodium ions rush into postsynaptic membrane
Membrane becomes depolarized - cannot experience action potential
Slight depolarization spreads throughout nerve (reducing threshold level)
What are the inhibitory effects that neurotransmitters have on post synaptic membrane?
Receptors trigger potassium ion channels to open
Potassium ions flow out - hyperpolarization occurs (more negative transmembrane potential)
How many signals can a single cell body receive from presynaptic membrane at same time?
As many signals as possible?
One of the functions of the cell body?
To integrate all of the incoming signals (combined affect of the signals spreads across cell body)
What happens if excietory stimuli is strong enough?
the depolarization will reach the point at which the axon is connected to the cell body
and an impulse will be generated
postsynaptic neuron will then return to resting potential
What happens after neurotransmitters have done their job?
Enzymes break it down and inactivate it
components are reabsorbed by presynaptic membrane
What is acetylcholine and what does it do?
Neurotransmitter that crosses a neuromuscular junction
It excites muscle membrane - causing depolarization and contraction of muscle fibre
If it remains in the synapse - muscle could not repolarize - remain contracted
What is sarin and how does it affect cholinesterase?
Nerve gas - blocks the release of cholinesterase into the neuromuscular junction
Build up of acetyl choline (critical muscles enter a state of paralysis and contract contraction)
What is cholinesteras?
Enzyme that is released into the synapse - where it breaks down acetylcholine
Allows protein receptors to close - membrane can repolarize in seconds
Function of Dopamine?
Affects the brain synapse in the control of body movement
Linked to sensations of pleasure
Effects of abnormal dopamine production?
Schizophrenia - individuals perception of reality is disordered
Parkinson’s disease - destroys neurons, causing tremors, slurred speech, other coordination problems
Function of serotonin?
Regulates body temperature and sensory perception
Involved in mood control
Effects of abnormal serotonin production?
brain synapses linked to depresssion
Function of endorphins?
natural painkillers in synapses in the brain
Effects emotional areas of the brain
Effects of abnormal endorphin production?
Deficiency linked to increased risk of alcoholism
Function of norepinephrine?
Used by the brain and some autonomic neurons
complements the actions of the hormone epinephrine (readies the body to respond to danger or other stressful situations?
Effects of abnormal production of norepinephrine?
High blood pressure - anxiety - insomnia
Deficiency linked to hunger cravings and exhaustion
