nervous system Flashcards
The central nervous system (CNS)
structural and functional centre of the entire nervous system. It consists of brain and spinal cord.
Integrates incoming sensory information
Evaluates the information
Initiates out going respond
The Peripheral Nervous System (PNS)
consists of the nerve tissue that lies in the periphery (outer regions) of the nervous system. These are cranial nerves and spinal nerves.
functional approach is divided Somatic and Autonomic.
Somatic system’s effector organ is voluntary (skeletal muscle)
Autonomic system’s effector organ is involuntary (smooth muscle and glands)
Two main type of cells made up the nervous system.
Neurons
Glia
neurons
excitable cells that conduct (transmits) the impulses that make possible all nervous system function (wiring of NS).
responsible for carrying information (or impulses) from one nerve to another. This nerve impulse also known as Action Potential (AP).
human brain 100 billion neurons
All neurons have a cell body
at least two processes - axon (only one branch) and dendrites (one, two or more branch).
Thread like extension often called nerve fibres.
Cell body (soma)
largest part. It has a nucleus, cytoplasm and various organelles such as mitochondria, ER and Golgi.
Dendrites
branched extensively like tiny trees
tiny branches receive information.
Axon
singe process of a neurone.
It emerges from cell body called axon hillock.
It can be long as 1m
has one or more side branches at the end.
The tip of axon have swellings called synaptic knobs or Synaptic button.
Each synaptic knob contains many small sacs (vesicles).
contains a chemical molecules called a neurotransmitter.
Glia
serves various roles in supporting the function of neurons.
Astrocytes
star shape glia
largest and most numerous glia in the CNS.
Astrocytes feed the neurons by picking up glucose from the blood.
They recycle chemical transmitters.
Influence the neuronal growth.
webs of astrocytes “feet” attached to brain’s blood capillaries, forms the blood brain barrier (BBB).
Encephalitis
inflammation of the brain
Most commonly caused by a viral infections.
The virus replicates outside the CNS and gains entry to the brain either via blood stream (BBB is not functioning).
Sometimes the virus also travel along the olfactory pathways.
Microglia
very small cells in the CNS.
stationary.
inflamed or degenerating brain tissue, they get enlarge and move about to get rid of cellular debris.
the immune cells of the brain tissue.
Ependymal cells
resemble epithelial cells.
line fluid filled cavities in the brain and spinal cord.
They are responsible for producing the fluid (cerebrospinal fluid).
They have cilia on their surface that help keep the fluid circulation.
Oligodendrocytes
smaller than astrocytes and have fewer processes.
Oligodendrocytes means “cell with few branches”.
Oligodendrocytes help hold nerve fibres together. produce the fatty myelin sheath around axons in the CNS.
Myelin sheath speed up nerve conduction
Multiple Sclerosis
chronic autoimmune disease of the CNS (the person’s own immune cells are responsible)
Immune cells target and destroy the myelin that wraps the nerves.
Loss of myelin reduces nerve conduction speed and
signals.
Signals are disturbed/abnormal.
The effects vary depending on which areas of the CNS are affected.
Sensory symptoms of Multiple Sclerosis
pain, tingling, numbness, visual and vestibular (balance) disturbances.
Motor effects - Multiple Sclerosis
difficulty moving, difficulty controlling movement, loss of accuracy of movement, weakening of muscles, tiredness.
Schwann cells
only found in the PNS. they have equivalent role with oligodendrocytes.
They also produce the myelin sheath.
Schwann cells also help debris removal and serve as guides for sprouts of regenerating axons after injury.
Meninges composed of three layers.
Dura Mater
Arachnoid Matter
Pia Mater
The Dura mater
strong fibrous tissue and serves as the outer layer of the meninges.
The Arachnoid matter
delicate, spider web like layer between.
The Pia Mater
delicate inner most layer of meninges. it is transparent and adhere to the brain tissue containing blood vessels.
Meningitis
(inflammation of meninges) is most often caused by bacteria or viruses.
Viral meningitis is self limiting with typically complete recovery.
Bacterial meningitis can have more serious effects.
Other pathogens such as fungi or parasite are also causes.
Bacterial meningitis is life threatening and less common than viral from.
Epidural Haematoma
Fracture of the skull can cause an accumulation of the blood outside the dura in the epidural space.
Cerebrospinal Fluid (CFS)
The CFS provides protection to brain and spinal cord.
present around the organs and within them.
When production of CFS exceeds resorption, hydrocephalus (also known as water in brain) results.
Hydrocephalus
excessive accumulation of Cerebrospinal fluid (CFS) in
the ventricles.
When fluid builds inside the brain, causes pressure which compress the nervous tissue and dilate ventricles.
Due to :
Increased CFS production or
CFS obstruction (blockage in the ventricles) or
Decreased CFS absorption
The compression of the nervous tissue usually results in irreversible brain damage.
Peripheral Nervous System
A- Cranial Nerves
B- Spinal Nerves
C- Ganglia
Brain
The brain is one of the largest organ in the adults.
Contains of 100 billions neurons and glia.
It weight about 1.4kg (3 pounds).
Consists of two halves ( the left and right cerebral hemispheres).
Divisions of the brain
A- Cerebrum
B- Diencephalon
C - Brain Stem
D- Cerebellum
Cerebrum
largest and upper most part of the brain. It looks wrinkly, hills are called gyri (gyrus), where as groves called sulci (sulcus).
These increase surface area of the brain. if we open up all cerebrum
If the groves are deeper called fissures.
cerebral hemisphere lobes
Frontal lobe, parietal lobe, temporal lobe and occipital lobe. there is also hidden lobe called insula
Function of the Cerebrum
Consciousness, thinking, memory, sensation, emotion and willed movements
Diencephalon
The small but important part of the brain, between brain stem and the cerebrum.
Diencephalon 3 major structures
the thalamus, the hypothalamus and epithalamus.
Thalamus
A dun-belled section of the grey matter. Functions as
1- Relays sensory information
2- Associates sensations with emotions
3- Regulates level of consciousness
Hypothalamus
located under the thalamus. It is small but one of the most important brain structures.
what does hypothalamus control
virtually all internal organs and regulates the autonomic nervous system.
It controls the heart beat, constriction and dilation of the blood vessels, releasing hormones, maintaining body temperature, regulation of the water balance, sleep cycle, control of appetite and many emotion
Epithalamus
Tiny mass protruding from the back of the diencephalon called pineal
gland.
It secretes melatonin (time keeping) hormone.
helps the body’s clock “on time” with daily, monthly and seasonal cycles of sunlight and moonlights.
Brain Stem
brain stem has three parts:
midbrain, pons and medulla oblongata.
All three parts function as two way conduction paths. Sensory impulses
up from spinal cord to the brain regions, motor impulses down from the
brain to the spinal cord.
many important reflex centres located in the brain stem.
The cardiac, respiratory and vasomotor (collectively called the vital
centres) are located in the medulla. Impulses from these centres control
heart beat, respiration and blood vessel diameter.
Parkinson’s disease (PD)
Most common disease of midbrain
PD is characterised by muscular rigidity, loss of facial expression, tremor,
a slow shuffling gait and general lack of movement. Usually occurs after
age 55.
PD is caused by the loss of neurons in the substantial nigra (in the midbrain).
These neurons contain dopamine neurotransmitter which
regulate motor activity. However, cause of this neuronal death in PD is
unknown.
Cerebellum
second largest part of the brain.
Similar to the brain it has also wrinkly surface. The grey matter is outer layer. White matter tracts form most of interior.
These tracts branch in a treelike pattern called the “arbor vitae” meaning “living tree”. The cerebellum plays an essential role in coordinated movements, maintain equilibrium (balance) and sustain normal posture.
