[LEC 5] Central Nervous System

Nervous system

reveals that the body consists of millions of small structures that perform a multitude of different activities

Brain

Nervous tissue within the cranium

Spinal cord

Extension of nervous tissue within the vertebral column

Nerves

Nervous tissue that reaches out from the brain and spinal cord to the rest of the body.

Endocrine system and the nervous system

Two main communications systems

Central nervous system

consists of the brain and spinal cord

Peripheral nervous system

consists of nerves of the body

Cranial nerves

12 pairs of nerves

Spinal nerves

31 pairs of nerves

Autonomic nervous system

It includes peripheral nerves and ganglia

Ganglia

a group of cell bodies outside the central nervous system that carry impulses to involuntary muscles and glands

Sensory

afferent

Motor

efferent

Associative

interneurons

Dendrites and axons

extensions of cytoplasm from the cell body

Myelin sheath

specialized covering of the axon

myelin

also called **white matter**

Nodes of Ranvier

an area where no myelin is present

Axons

carry messages away from the cell body

Dendrites

carry messages to the cell body

Neuroglia or glial cells

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* Maintain the extracellular environment around neurons, improve signal conduction in neurons
* Protect neurons from pathogens

Neuroglia or glial cells

* Sometimes referred to as “nerve glue.”
* Do not carry nerve impulses.

Astrocytes

\- Have many processes extending from the cell body

\- Supporting cells for the neurons in the CNS

\- Contribute to the blood-brain barrier

Microglia

\- Smaller than most glial cells

\- May have originated as macrophage that become part of the CNS during early development

\- Function is similar to macrophage

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**Oligodendrocytes**

\- Insulates axons in the CNS

\- Few processes extend from the cell body

\- Produce myelin to insulate an axon

Ependymal cells

\- Filter blood to make cerebrospinal fluid (CSF)

\- In contact with the choroid plexus which delivers blood for filtration

Schwann cell

\- Insulate axons with myelin in the PNS

\- Different from oligodendrocytes in that it wraps around a portion of only one axon segment and no other

\- Its nucleus and cytoplasm are on the edge of the myelin sheath

Satellite cell

\- Surround the cell bodies of neurons in the PNS

\- Provide support (similar to astrocyte, except for forming the BBB)

Neurons

Have the ability to react when stimulated and the ability to transmit a disturbance to distant points

Cell body

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*  Also called soma
* Region where its nucleus is located
* From which cellular activity like repair or cell membrane recycling is controlled

Nissil bodies

Rough ER in the cell body for protein production

Dendrites

*  Short projections of the cell body.


* Receive most of the input or stimuli
* Marks the receptive region of the neuron
* Usually highly branched processes

Axon

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* Emerge from the cell body at the **axon hillock**
* Often wrapped by myelin sheaths, leaving exposed areas (**node of Ranvier**) between segments of myelin

Myelin

acts as electrical insulation, speeding information conduction down the neuron

Initial segment

The first section of the axon where an action potential is generated

Terminal end

* Where information from this neuron is transferred to another cell


* Has several branches, each with a **synaptic end bulb** to store chemicals needed for communication

Synapse

The site of communication between a neuron and its target cell

Multipolar neurons

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* Have multiple processes emerging from their cell bodies
* Have dendrites attached to their cell bodies and often, one long axon.

Multipolar neurons

Motor neurons

Bipolar cells

* Have two processes, which extend from each end of the cell body, opposite to each other


* One is the axon and one the dendrite
* Not very common
* Found mainly in the olfactory epithelium and the retina in the eye

Unipolar cells

* Have one long axon emerging from the cell body but the cell body is located at neither end of that axon


* At one end of the axon are dendrites, and at the other end, the axon forms synaptic connections with a target cell
* Exclusively sensory neurons and have their dendrites in the periphery where they detect stimuli.

Efferent neuron or Motor neuron

carry messages from the brain and spinal cord to  the muscles and glands

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Associative neurons or interneurons

carry impulses from the sensory neurons to the motor neurons

Membrane excitability

Nerves carry impulses by creating electric charges in a process known as

synaptic cleft

The space between the axon and a dendrite

Neurotransmitters

chemical substances that make it possible for messages to cross the synapse of a neuron to a target receptor.

Impulse

 Travels along the axon to the end where the neurotransmitter is released.

Acetylcholine

The neurotransmitter between muscle cells and the nervous system cells

Brain

Highly developed, complex, and intricate mass of soft nervous tissue. 

Cerebral cortex

* Outer cortex, gray


* Highest center of reasoning and intellect

Deeper part of the cerebral cortex

Consists of myelinated nerve tracts, white

Dura Mater

* Outer brain covering, which lines the inside of the skull.
* Tough, dense membrane of fibrous connective tissue containing an abundance of blood vessels.

Subdural space

Between the dura mater and the arachnoid mater

Arachnoid mater

Middle layer; resembles a fine cobweb with fluid-filled spaces.

Cerebrospinal fluid

The subarachnoid space between the arachnoid and pia mater is filled with **_________,** produced within the ventricles of the brain.

Cerebrospinal fluid

This fluid acts as a shock absorber as well as a source of nutrients for the brain.

Pia mater

Covering the brain surface itself, consisting of blood vessels held together by fine areolar connective tissue.

Cerebral ventricles

The brain contains four lined cavities filled with cerebrospinal fluid

Right and left lateral ventricles

The two largest, located within the cerebral hemispheres, are known as

Third ventricle

Placed behind and below the lateral ventricles

Interventricular foramen

Connects the right and left ventricles to the third ventricles

Fourth ventricle

Situated below the third, in front of the cerebellum, and behind the pons and the medulla oblongata (brain stem).

Cerebral aqueduct

The third and fourth ventricles are interconnected via a narrow canal called this

Choroid plexus

Each of the four ventricles contains a rich network of blood vessels of the pia mater, referred to as the ________

Choroid plexus

In contact with the cells lining the ventricles, which helps in the formation of cerebrospinal fluid

Cerebrum

* largest part of the brain. 


* It occupies the whole upper part of the skull. 

Cerebral cortex

* A continuous layer of gray matter that wraps around either side of the forebrain


* Responsible for the higher functions of the nervous system

Longitudinal fissure

Divides the cerebrum into two hemispheres

Corpus callosum

The middle region of the two hemispheres is held together by a wide band of axonal fibers called the _______

Basal nuclei

* For cognitive processing, and associated with planning movements


* Located at the base of the forebrain and top of the midbrain
* Associated with voluntary motor movement control, learning, eye movement, cognition and emotion

Basal forebrain

Important in learning and memory

Limbic cortex

Involved in emotion, memory and behavior

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Brodman’s areas

Anatomic division of the cerebral cortex into 52 separate regions based on histology

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Area 17 and 18

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Primary visual perception/ cortex

Area 41 and 42

Primary auditory sensation

Area 22 and 23

Primary auditory cortex

Area 3, 1 and 2 (postcentral gyrus)

Primary somatosensory cortex

Area 4 (precentral gyrus)

Primary motor cortex

Longitudinal Fissure

a deep groove that divides the cerebrum into two hemispheres

Transverse Fissure

divides the cerebrum from the cerebellum

Central Sulci

divides the frontal lobe from the parietal lobes

Lateral fissure

divides the frontal lobe and temporal lobes

Parieto-occipital fissure (sulci)

the least obvious of all the fissures, serves to separate the occipital lobe from the parietal and temporal lobes, although no definite demarcation between these two lobe exists.

Parietal lobe

\-Located behind the frontal lobe. 

\-It receives and interprets nerve impulses from the sensory receptors for pain, touch, heat, cold, and balance. -It further helps determine distance, sizes, and shapes.

Occipital lobe

\- Located over the cerebellum; houses the visual area controlling eyesight.

Temporal lobe

\- Located beneath the frontal and parietal lobes. 

\- The anterior portion is occupied by the olfactory (smell) area, and the temporal lobe contains the auditory area. 

Wernicke area

The **_______** of the temporal lobe is the central language area for speech understanding and comprehension.

Diencephalon

* located between the cerebrum and the midbrain.


* Connection between the cerebrum and most of the rest of nervous system

Thalamus

A collection of nuclei that relay information between the cerebral cortex and the periphery, spinal cord or brain stem

Frontal lobe

\- Forms the anterior portion of each hemisphere. 

\- It controls voluntary muscle movement.

Thalamus

Damage to the ________ may result in increased sensitivity to pain or total loss of consciousness

Thalamus

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* found deep inside each of the cerebral hemispheres, lateral to the third ventricle. The thalamus acts as a relay station for incoming and outgoing nerve impulses. 
* receives direct or indirect nerve impulses from the various sense organs of the body

Hypothalamus

* lies below the thalamus. 


* part of the limbic system and is considered the “brain” of the brain.

Cerebellum

* The “little brain”
* located behind the pons and below the cerebrum

Vermis

Central portion that both hemispheres of the cerebellum connect to

Arbor vitae

The white matter within the cerebellum is marked with a treelike pattern called ___________

Peduncles

The cerebellum communicates with the rest of the central nervous system by three pairs of tracts called ________

“incoming” axons

* carry nerve messages into the cerebellum


* carry messages to the cerebellum regarding movement within joints, muscle tone, position of the body, and tightness of ligaments and tendons.

“outgoing” axons

* transmit messages out of the cerebellum. 


* carry nerve messages to the different parts of the brain that control skeletal muscles.

Brainstem

* Emerges from the ventral surface of the forebrain as a tapering cone


* Connects the brain to the spinal cord