11.1 Structures and Processes of the Nervous System Flashcards
Define homeostasis
Stability within the body
List two examples of involuntary processes
- Breathing
- Heart rate
What is the motor pathway?
A pathway made up of nerves that send sensory information from the CNS to muscles and glands
Explain the Somatic Nervous System
The SNS is part of the peripheral nervous system that controls voluntary movements and relays sensory information. It consists of motor neurons and sensory neurons that connect the CNS to muscles and skin.
Sensory neurons carry signals from sensory receptors to the central nervous system
Motor neurons transmit signals from the CNS to skeletal muscles allowing for voluntary movement
What is the peripheral nervous system and what does it do?
The peripheral system is a system made up of nerves and ganglia outside the center (brain and spinal cord).
It sends sensory messages to the CNS via nerves
It sends sensory information from the CNS to muscles and glands
Define sensory pathways
Pathways made up of nerves that carry sensory messages to the CNS
Explain the Automatic Nervous System
The ANS is a division of the peripheral nervous system responsible for regulating involuntary physiological functions in the body.
It is divided into two main branches
1. The Sympathetic Nervous System
2. The Parasympathetic Nervous System
List the types of cells found in the NS
- Neurons
- Glial cells
What are neurons?
Specialized cells that can receive and send electrochemical signals called impulses and respond to stimuli.
What are glial cells?
“Nanny cells” that support, nourish, and protect neurons.
List the structures that make up the Central Nervous Syetem and its role in the body
- Brain
- Spinal cord
The role of the CNS is to receive information from the senses, to integrate it, and then to generate a response.
What are the categories under the automatic nervous system and what do they do?
Sympathetic and parasympathetic nervous system work in opposition to regulate the involuntary processes of the body
What is the name of the tissue that neurons are organized into?
Nerves (covered by a connective tissue)
What are the three main neurons that form basic impulse pathways?
- Sensory neurons
- Interneurons
- Motor neurons
What are the three overlapping functions that make up the NS?
- Sensory input
- Integration
- Motor output
Describe sensory input
Sensory neurons carry info from sensory receptors (senses) to the CNS
Describe intergration
Integrates and processes incoming sensory information and relays outgoing motor information
Describe motor output
Moto neurons transmit information from the CNS to effectors
What are reflexes?
Quick, automatic responses to a stimulus
What is a reflex arc?
A pathway that controls a quick, automatic response to a stimulus.
It bypasses the brain for faster action.
How many neurons do withdrawal reflexes use?
Involves three neurons: a sensory neuron, an interneuron, and a motor neuron
Why do we not feel pain before we respond to stimuli?
The impulse is carried from the sensory neuron to the interneuron 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
The brain processes what has happened after reflex - hence why we feel pain after
Describe the dendrites appearance
Highly brancehed, numerous, short, branching terminals
What is the benefit of dendrites being numerous and highly branched?
Increased surface area to receive information
What is the function of dentrites?
They receive impulses from other neurons and sensory receptors, relaying impulses to the cell body
Describe the appearance of the cell body?
Contains a nucleus nd is the site of the cell’s metabolic reactions
What is the function of the cell body?
It processes input from dendrites and relays it to the axon (where an impulse is initiated)
What is the function of an axon?
Area in the neuron where the nerve impulse takes place (where electricity is generated and transmitted)
What is the function of the axon terminal?
It releases chemical signals in the space between it and the sensory receptors on other dendrites
It does this to communicate with adjacent neurons, glands, or muscles
How long are axons?
They range in length depending on where in the body they are located (from 1mm to 1m)
Which nerve in the body contains the longest axon?
The sciatic nerve in the leg
It contains neuronal axons that extend from the spinal cord to the foot (over 1m)
Describe the appearance of the myelin sheath?
Fatty, insulating layer that encloses the axons of some neurons
Gives axons a white, glistening appearance
What is the function of the myelin sheath?
It protects myelinated neurons and speeds the rate of nerve impulse transmission
What forms myelin?
Schwann cells
How do Schwann cells form myelin?
By wrapping themselves 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 unmyelinated?
Mostly myelinated
Who was Luigi Galvani?
An Italian physicist and anatomist who discovered the electric nature of nerve tissue
What did A.L Hodgkin perform on and why?
A squid because they have bigger axons so the potential difference across the membrane was easier to measure
How is the potential difference measured?
One would insert an electrode into an axon and read potential difference from specialized voltameter
How does nerve conduction differ from electrical conduction?
Nerve conduction is slower and more complex as it depends on the movement of ions across the cell membrane of an 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 and 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 the outside, positivee on the inside)
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 impermeable to
Large protein molecule and small negatively charge ions (chloride)
What is the most important contributor to the separation charge and the resulting electrical potential difference across the
membrane?
The sodium-potassium pump
What is the sodium-potassium exchange pump?
System involving carrier proteins in the plasma membrane - that uses the energy of ATP to:
Transport 3 sodium ions out and 2 potassium ions in
Where is the energy that the resting membrane potential generated stored?
In the electrochemical gradient across the membrane, where it waits for an impulse to occur
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?
When 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 between -70mV and -55mV has no effect (doesn’t meet the threshold potential)
It either fully responds to stimuli or doesn’t
Which depolarization measurements will produce identical action potentials?
Depolarization from -55mV up to 0.
What happens when transmembrane potential at the nodes of Ranvier reach threshold? (Think sodium ions)
Voltage gated sodium ions open
Makes 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 happens to the sodium ions when an action potential occurs, the sodium gate has been closed, and there is nowhere 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 it reaches neighboring nodes of Ranvier the positive charge reduces the net negative charge in the membrane and the nodes of Ranvier become depolarized to threshold
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 CNS
Neurons can no longer transmit electrochemical signals between the brain and body
What is autoimmune disease and what are the symptoms?
An autoimmune disease occurs when the body’s immune system breaks down the myelin sheath
Symptoms include blurred vision, loss of balance, muscle weakness, fatigue, and slurred speech
What is a synapse?
The connection between two neurons, or a neuron and an effector
What is a neuromuscular conjuction?
The synapse between a motor neuron and a muscle cell
What is the synaptic terminal?
The end of the axon that 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 and release them into the synaptic cleft (through exocytosis)
What do the neurotransmitters bind to when they reach the postsynaptic membrane?
Receptor proteins
How long does it take the neurotransmitters to reach the postsynaptic neuron?
0.5 to 1mS
What do receptor proteins trigger?
Ion-specific channels to open, depolarizing the membrane
If the threshold potential is reached an 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 the postsynaptic membrane
Membrane becomes depolarized (cannot experience action potential)
Slight depolarization spreads throughout the 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)
One of the functions of the cell body?
To integrate all of the incoming signals (combined effect of the signal spreads across the cell body)
What happens if excitatory 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, the 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 then reabsorbed by the presynaptic membrane
What is acetylcholine and what does it do?
A neurotransmitter that plays a key role in both the CNS and PNS
It excites the muscle membrane, causing depolarization and contraction of muscle fiber
If it remains in the synapse muscle cannot repolarize - remains contracted
What is sarin and how does it affect cholinesterase?
Nerve gas that blocks the release of cholinesterase into the neuromuscular junction
What is the function of Dopamine?
It affects the brain synapse in the control of body movement and is linked to sensations of pleasure
What are the effects of abnormal dopamine production?
Schizophrenia - individual’s perception of reality is disordered
Parkinson’s disease - destroys neurons, causing tremors, slurred speech, and other coordination problems
What is the function of serotonin?
Regulates body temperature, sensory perception, and is involved in mood control
What are the effects of abnormal serotonin production?
Brain synapses linked to depression
What are the functions of endorphins?
They act as natural painkillers in the synapses of the brain and effect the emotional areas of the brain
What are the effects of abnormal endorphin production?
Deficiency linked to increased risk of alcoholism
What is the function of norepinephrine?
Norepinephrine complements the actions of the hormone epinephrine in readying the body to respond to danger or other stressful situations
What are the effects of an abnormal production of norepinephrine?
High blood pressure, anxiety, insomnia, and a defiency linked to hunger cravings and exhaustion
