Nervous 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 structure

Cross section of myelin sheaths that surround axons

3 main types of nerve cells sensory neuron relay neuron motor neuron

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

Relay neuron Carries impulses from sensory nerves to motor nerves.

Motor 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),cerebrum  cerebellum, and the medulla oblongata (these latter two are "part of the unconscious brain").cerebellummedulla oblongata

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. 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.midbrain pons

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

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.Nervous SystemEndocrine 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.reflexes  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.