Anatomy 3: Overview of the Nervous System Flashcards
What is the function of the nervous system?
The nervous system is the master controlling and communicating system of the body. It gathers information about what is occurring inside and outside the body. It then processes this information and makes decisions about what should be done moment by moment.
What is nervous tissue composed of?
Nervous tissue consists of neurons and supporting cells. Neurons transmit, receive and process information.
What is a neuron?
The neuron is the functional unit of the nervous system. They are sensitive to stimuli (mechanical, thermal or chemical) and are able to conduct messages.
What is the structure of a neuron?
Extending from the cell body (soma, perikaryon) are:
- Numerous branching processes called dendrites, which receive electrochemical stimuli from other cells at synapses
- The axon, a long singular process that does not branch close to the body and transmits electrical signals away from the cell body, towards another neuron.
- The axon is normally covered by a myelin sheath (lipid made by Schwann cells), which insulates the axons and speeds up electrical conduction along it.
- Near the end of the axon, it splits into small branches called telodendria. These end as small swellings (axon terminals or terminal boutons)
What are the two parts of the nervous system?
1. Central Nervous System:
The brain and spinal cord.
2. Peripheral Nervous System:
Everything else! The nerves and ganglia outside the brain and spinal cord. The PNS has voluntary (somatic) and involuntary (autonomic)
components. This includes both afferent (sensory) and efferent (coming) afferent means carrying sensations TO the spinal cord, whereas efferent means carrying sensations away from the spinal cord!
What are the components of the peripheral nervous system?
- Somatic (voluntary) component
- Autonomic (involuntary) component
What is the purpose of the somatic (voluntary) component of the nervous system?
Somatic (voluntary) component:
responsible for innervating (supplying, projecting) the skin, skeletal (striated) muscle, bones and joints – essentially dealing with the body wall and the limbs, being a volunatry process.
- The skin, bones and joints are all involved in sensory information to the spinal cord or brain
- Muscle involves commands going out to the muscle from the spinal cord (other way!).
What is the purpose of the Autonomic (involunary) component?
Autonomic (involuntary) component:
responsible for innervating the involuntary parts of the body, including internal body organs (viscera) including blood vessels and glands.
- Can be further divided into the sympathetic and parasympathetic parts.
In the PNS, there is a sensory (afferent) division and a motor (efferent) division. What are the subdivivisions of each?
Sensory (Afferent) Division
Somatic sensory
Visceral sensory
Motor (Efferent) Region
Somatic Motor
Visceral Motor
What is the function of the Somatic Sensory division?
Somatic sensory: Sensory that comes from the body or the limbs, including a wide range of senses:
Touch Pain Pressure Vibration
Temperature Proprioception (knowing position of limbs in space, important for use of muscles)
What is the function of the Visceral Sensory Division?
Visceral sensory: The reason most patients will see a doctor, for abnormality. Cardiac pain, carried back to spinal cord and then brought to conscious awareness by visceral sensory fibres – which come in lots of different shapes and sizes. Visceral sensory fibres include:
Stretch Pain Temperature Chemical changes (to be received as pain) Nausea and hunger
What is the function of the Somatic Motor division?
Somatic motor: The reason we are able to move our limbs is because of somatic motor function – we can voluntarily contract skeletal muscle, due to the innervation of all skeletal muscles, due to innervation from the spinal cord and cranial nerves.
What is the function of the Visceral Motor division?
Visceral motor: There is also smooth muscle (involuntary) control, and this includes cardiac muscles and glands, which are subconcious – all covered by visceral motor.
The CNS is largely enclosed in the bony framework. Inside the skull, there are lots of membranes that surround and protect the brain. What are they called?
Meninges (They support and protect the brain)
What are the layers of the meninges?
Dura mater – outside membrane
Arachnoid – delicate membrane (like a spider’s web!) Below the arachnoid there is a subarachnoid space – which has a fluid in it – CSF!
Pia mater – on the surface of the brain surface.
Why is there a discrepancy in the spinal segement and nerve exit locations?
Because the spinal nerve is shorter then the vertebral column, it means that some of the spinal nerves actually have to run some distance before they can leave the vertebral column!
- At the top, the 1st cervical nerve comes out and the 1st cervical nerve.
- As you move down, the nerve must travel further and further before it leaves – but the nerve’s name is based on which vertebral column it leaves below!
What is the spinal segment, and what are its components?
The spinal segment is the area of the spinal cord that gives rise to the rootlets of one spinal nerve.
There are 2 sets of rootlets – and one at the back, called dorsal rootlets , and one at the front, called ventral rootlets, which all join together to form a spinal nerve.
What is the basic structure of a spinal nerve, and the surrounding structures?
What is the function of the Parasympathetic path?
The parasympathetic division is often referred to things related to being in the VEGETATIVE STATE - tends to be about conserving energy or taking energy stores on board to be used late. It is responsible for storage, conserving energy, taking on board nutrients and bringing the body back to a state of rest.
The parasympathetic path is also referred to as the craniosacral outflow. There is a flow of control through cranial nerves (nerves attached to the brain stem) and sacral nerves (nerves attached to sacral part of spinal nerve).
What is the difference betweenj the autonomic and somatic motor systems?
Somatic (voluntary):
A somatic motor neurone is a voluntary neurone that has a cell body within the spinal cord (ventral horn) which sends its axon out through the ventral root to skeletal muscle.
The somatic motor system only has 1 nerve cell that goes straight to the target tissue.
Autonomic (involuntary):
The autonomic outflow comes from a different flow. The autonomic (in this case sympathetic) neurone is connected to the lateral horn , with a fibre that heads out to a GANGLION, instead of going straight to the target structure (smooth muscle or gland etc.).
There is usually 1 pre-ganglionic neurone in the spinal cord and then a postganglionic neurone inside a cluster of nerve cell bodies, which then sends an axon out to the body being supplied!
The ANS usually has at least 2 nerve cells in the chain of th e outflow from the spinal cord to the target organ.
What is the sympathetic trunk?
- A collection of nerve cell bodies (the ganglia) lie alongside the entire length of the vertebral column. The sympathetic trunk has very fine process that connect them to the spinal nerves.
- Ramus communicans , connects the sympathetic trunk to the spinal nerve.
What is happening in this picture?
As can be seen, there is a pre-ganglionic nerve fibre that comes out of the spinal cord, crosses the white ramus communicans to go the ganglia in the sympathetic trunk, where it then synapes to a post ganglionic nerve fibre, passes back along the gray ramu s communicans , and then heads out to the target tissue.
