Division of nervous system Flashcards
The essential purpose of the nervous system is to:
receive and process information from sense organs
to bring about responses to the information received.
The two main parts of the nervous system are the:
1.Central nervous system (CNS)
consists of the brain and spinal cord
2.Peripheral nervous system (PNS)
consists of nerves that connect the CNS with the receptors, muscles and glands
and ganglia (groups of nerve cell bodies outside the brain and spinal cord)
The peripheral nerves arise from the brain and the spinal cord:
cranial nerves = 12 pairs of nerves arise from the brain
spinal nerves = 31 pairs of nerves arise from the spinal cord.
3 types of nerve
Sensory fibres = fibres that carry impulses into the CNS
Motor fibres = Those that carry impulses away from the CNS
Mixed nerves contain fibres that carry impulses into and away from CNS
Are all cranial nerves mixed nerves ?
No. Most cranial nerves are mixed nerves. A few cranial nerves carry only sensory impulses or only motor impulses.
Are all spinal nerves mixed nerves ?
All spinal nerves are mixed nerves and each is joined to the spinal cord by two roots.
Describe ventral root
The ventral root contains the axons of motor neurons that have their cell bodies in the grey matter of the spinal cord.
Describe the dorsal root
The dorsal root contains the axons of sensory neurons that have their cell bodies in a small swelling on the dorsal root known as the dorsal root ganglion
Explain the afferent sensory division
Carry impulses into the CNS
1. somatic sensory neurons
sensory nerve cells from receptors in the skin and around the muscles and joints
- visceral sensory neurons
sensory nerve cells that take impulses from the internal organs into the CNS
Explain the efferent motor division
Carry impulses away from the CNS
1.Somatic division
takes impulses from the CNS to the skeletal muscles
2.Autonomic division
carries impulses from the CNS to heart muscle, involuntary muscle and glands. Further subdivided into:
sympathetic division
parasympathetic division
Function of autonomic nervous system
Involved in many of the mechanisms that keep the internal environment constant.
How does autonomic nervous system operates?
without conscious control
How are the autonomic nervous systems regulated by?
regulated by groups of nerve cells in the medulla oblongata, hypothalamus and cerebral cortex.
Which part does nerve fibres of ANS make up ?
Nerve fibres of the ANS make up part of the spinal nerves and part of some of the cranial nerves.
Where does the nerve fibres of ANS carry impulses to ?
They carry impulses to the heart muscle, other muscles of the internal organs and the glands.
How many motor neurons relay impulses from CNS to effector in the autonomic pathway ?
2
Where is the motor neurons in the autonomic pathway?
The first neuron’s cell body is in the CNS, but the cell body of second neuron is in a ganglion (group of nerve cell bodies outside the CNS)
How many motor neurons relay impulses from CNS to effector in the somatic pathway ?
1
Where is the motor neurons in the somatic pathway?
nerve cell body in grey matter of spinal cord
Most organs under autonomic control receive two sets of nerve fibres, which are?
Sympathetic fibres - produce responses that prepare the body for strenuous physical activity (fight-or-flight responses). Sympathetic nerve endings release noradrenaline
Parasympathetic fibres - produce responses that maintain the body during relatively quiet conditions. Parasympathetic nerve endings release acetylcholine
What is the neurotransmitter that carries the message from neuron to the skeletal muscle in somatic nervous system?
acetylcholine
At rest, parasympathetic stimulation keeps heart rate to
~ 70 to- 80 beats per minute.
In threatening situation which division is more dominant?
sympathetic becomes dominant.
Explain the actions of response in sympathetic stimulation
- The rate and force of contraction of the heart increase, with a consequent increase in blood pressure.
- Blood vessels in organs involved in strenuous activity – such as the skeletal muscles, heart and liver – dilate.
- Blood vessels of organs not involved in activity – such as the kidney, stomach, intestines and skin – constrict.
- Airways in the lungs dilate and the rate and depth of breathing increases.
- Blood glucose level rises, because the liver converts more glycogen into glucose.
- Secretion from sweat glands increases.
- The adrenal medullae release the hormones adrenaline and noradrenaline, which intensify and prolong the above responses.
The difference in nervous and hormonal coordinations :
- Nervous responses are more rapid because nerve impulses travel rapidly along nerve fibres.
Hormonal responses are slower, because hormones are transported in the bloodstream.
3. Nervous messages are an electrochemical change that travels along the membrane of a neuron.
Endocrine messages are chemicals (hormones) that are usually transported by the blood
4. Nerve impulses travel along a nerve fibre to a specific part of the body and often influence just one effector
Hormones travel to all parts of the body, are carried by the blood and often affect a number of different organs.
The similarities of hormonal and nervous coordinations :
Some substances function as both hormones and neurotransmitters. Examples: noradrenaline, antidiuretic hormone and dopamine.
Some hormones such as oxytocin and adrenaline are secreted by neurons into the extracellular fluid.
Some hormones and neurotransmitters have the same effect on the same target cells.
Example: noradrenaline and the hormone glucagon both act on liver cells to cause glycogen to be broken down into glucose.
