Nervous SystemNervous System

By the end of the lesson you should be able to

Describe the transmission of impulses from senses to central nervous system and back to muscles.

Describe the reflex action and the pathway of the reflex arc.

Describe the function of reflex response. Describe the role of the central nervous

system.

nervous system

Cells of the Nervous System

Neuron- transmit impulses, amitotic( Lack centrioles)

Neuroglia/ “Glial”- hold the functioning neurons

Basic nerve cell Basic nerve cell structurestructure

Cross section of myelin sheaths that surround axons

3 main types of nerve 3 main types of nerve cellscells

sensory neuron

relay neuron

motor neuron

Sensory neuronsSensory neurons

Carries impulses from receptors e.g pain receptors in skin to the CNS( brain or spinal cord)

Relay neuronRelay neuron

Carries impulses from sensory nerves to motor nerves.

Motor neuronMotor neuron

Carries impulses from CNS to effector e.g. muscle to bring about movement or gland to bring about secretion of hormone e.g ADH

Types of Glial Cells

Astrocytes- hold neurons and blood vessels

Microglia- capable of phagocytosis, “Police force and janitorial service”

Oligodendroglia- hold nerve fibers together, produce myelin sheath

Transmission of signals

The Synapse

Neurotransmitters

small molecules, some are even hormones. The time for neurotransmitter action is between

0,5 and 1 millisecond. Neurotransmitters are either destroyed by specific

enzymes in the synaptic cleft, diffuse out of the cleft, or are reabsorbed by the cell.

More than 30 organic molecules are thought to act as neurotransmitters. The neurotransmitters cross the cleft, binding to receptor molecules on the next cell, prompting transmission of the message along that cell's membrane.

neurotransmitters are active for only a short time. Enzymes in the cleft inactivate the neurotransmitters. Inactivated neurotransmitters are taken back into the axon and recycled.

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Main parts of the Brain

cerebrum (seat of consciousness), cerebellum, and the

medulla oblongata (these latter two are "part of the unconscious brain").

The major brain areas and lobes

The occipital lobe (back of the head) receives and processes visual information.

The temporal lobe receives auditory signals, processing language and the meaning of words.

The parietal lobe is associated with the sensory cortex and processes information about touch, taste, pressure, pain, and heat and cold.

The frontal lobe conducts three functions:

-motor activity and integration of muscle

activity -speech

-thought processes

Cerebrum

Cerebral hemispheres are divided by the corpus callosum .

. governs intelligence and reasoning, learning and memory.

Cerebellum

The cerebellum is the third part of the hindbrain, but it is not considered part of the brain stem.

Functions of the cerebellum include fine motor coordination and body movement, posture, and balance.

Midbrain and pons

The midbrain and pons are also part of the unconscious brain.

Thalamus

The thalamus serves as a central relay point for incoming nervous messages.

Hypothalamus regulates

homeostasis It has regulatory

areas for thirst, hunger, body temperature, water balance, and blood pressure, and links the Nervous System to the Endocrine System.

The Spinal Cord

The gray matter of the spinal cord consists mostly of cell bodies and dendrites.

The surrounding white matter is made up of bundles of interneuronal axons (tracts). Some tracts are ascending (carrying messages to the brain), others are descending (carrying messages from the brain).

The spinal cord is also involved in reflexes that do not immediately involve the brain.

1Spinal Nerve 5Central Canal 2Dorsal Root Ganglion 6Grey Matter3Dorsal Root

(Sensory) 7White Matter 4Ventral Root (Motor)  

Protective membranes of the Spinal Cord

Dura Mater- tough tube that encases the two inner membranes (arachnoid and pia mater)•spinal fluid, commonly called cerebrospinal fluid (CSF). •cushions, protects and nourishes the spinal cord and nerve roots.