The NERVOUS System

Functions of the Nervous System Sensory senses stimuli Integrative Analyzes/interprets information about the stimuli it receives Motor responds to stimuli by some type of action muscular contraction glandular secretion

Nervous System Schematic

The Central Nervous System Consists of the brain and spinal cord Sorts incoming sensory information Generates thoughts and emotions Forms and stores memories Stimulates muscle contractions Stimulates glandular secretions

The Peripheral Nervous System Connects sensory receptors, muscles, and glands in the peripheral parts of the body to the central nervous system Consists of cranial and spinal nerves Afferent Neurons (Sensory) conduct nerve impulses from sensory receptors toward the CNS Efferent Neurons (Motor) conduct nerve impulses from the CNS to muscles and glands

The Somatic Nervous System Sensory neurons that convey information from the body to the CNS Motor neurons from the CNS that conduct impulses to the skeletal muscles

The Autonomic Nervous System Sensory neurons from the viscera that convey information to the CNS Efferent neurons that conduct impulses to smooth/cardiac muscle and glands Unconscious control Two divisions of the ANS Sympathetic Division - stimulatory effect Parasympathetic Division - inhibitory effect

Neurons The nerve cells responsible for the special functions of the nervous system sensing - remembering- thinking controlling muscle activity controlling glandular secretions Synapse - points between two neurons or between a neuron and an effector organ Neuromuscular Junction Neuroglandular Junction

Parts of A Neuron Cell Body (Soma) nucleus, cytoplasm, organelles Dendrites - processes protruding from the cell body. Receive impulses. usually very short AFFERENT FUNCTION Axons - long, thin process that transmits impulses usually myelinated EFFERENT FUNCTION

Neurons

Neuroglia Nervous system cells that support, nurture and protect the neurons Types of Neuroglia found in the CNS Astrocytes Oligodendrocytes Microglia Ependymal Cells Types of Neuroglia found in the PNS Neurolemmocytes (Schwann Cells)

Astrocytes Star-shaped cells with many processes Participate in metabolism of neurotransmitters Maintain K+ balance for generation of nervous impulses Participate in brain development Help form the blood brain barrier Provide a link between neurons and blood vessels

Oligodendrocytes Form a supporting network around the neurons (myelin sheath) within the CNS Cannot repair if damaged

Microglia Small phagocytic cells that protect the central nervous system by engulfing invading microbes Clears away debris from dead cells

Ependymal Cells Neuroglia cells that line the brain ventricles Line the central canal of the spinal cord Helps form and circulate cerebral spinal fluid

Neuroglia of the PNS Schwann Cells - Neurolemmocytes Cells responsible for producing the myelin sheaths around the PNS neurons Speeds up transmission of impulse Can repair if damaged

Myelination The process of developing or producing a Myelin Sheath Insulates the axon of a neuron Increases the speed of nerve impulse conduction CNS - oligodendrocytes PNS - neurolemmocytes (Schwann Cells) Diseases such as Tay-Sachs disease and Multiple Sclerosis involve destruction of the myelin sheaths around the nerve

Neurophysiology The transmission of nerve (electrical) impulses from nervous tissue to other nervous tissue, organs, glands, and muscles.

Neuron Membrane Potential Na+ is in higher concentration outside the cell and K+ is in higher concentration inside the cell.

Neuron Action Potential Na+ moves in and K+ moves out of the cell, causing a change in the polarity of the cell.

Transmission of Nerve Impulses An electrical event due to movement of ions across a membrane Also called an action potential Lasts about 1 msec (1/1000 of a second) Dependent upon diameter of the axon larger diameter axons - 0.4 msec (1/2500 sec) 2500 impulses per second smaller diameter axons - 4 msec (1/250 sec) 250 impulses per second

Neuron Impulse “Ion Exchange”

Types of Impulse Conduction Continuous Conduction - step by step depolarization of each area of the nerve typical of unmyelinated nerve fibers Saltatory Conduction - the jumping of an action potential along the axon Nodes of Ranvier

Gray and White Matter White Matter -myelinated processes from many neurons Gray Matter - unmyelinated nerve cell bodies, axons, dendrites, ganglia, and axon terminals Appears gray because of lack of myelin

https://www.youtube.com/watch?v=7EyhsOewnH4

Reflexes Fast, predictable, automatic responses to changes in the environment Somatic Reflexes - involve skeletal muscles Visceral (Autonomic) Reflexes - involve responses of smooth muscles, the heart, and glands Involve the spinal nerves

The Reflex Arc A response by the body involving only the body segment being affected and the spinal cord Brain does not have to be involved 5 parts--Sensory receptor--->sensory neuron---> integrating center (processing center)---> motor neuron--->effector (completes action) Know for test!

The BRAIN 1

The BRAIN One of the largest organs in the body Controls all mental functions Component of the CNS Composed of over 100 billion neurons Comprises 2-3% of body weight Utilizes over 20% of body’s energy 5

Major Divisions of the BRAIN CEREBRUM - occupies most of the cranium and is divided into right and left halves called hemispheres Cerebral cortex Gray matter of the brain Gyrus-elevations Sulcus-grooves Fissure-deep grooves Corpus collosum connects hemispheres 6

CEREBELLUM - the posterior-inferior portion of the brain Coordinates skeletal muscle movements Balance

DIENCEPHALON - located above the brainstem Composed primarily of the: Thalamus (emotional center) Hypothalamus (connection between brain and endocrine system) Regulates vitals

BRAIN STEM - consists of the: medulla oblongata (controls vitals; coughing, sneezing, swallowing, vomiting) the pons (regulates rate and depth of breathing) the midbrain (reflex center for hearing and vision) it is continuous with the spinal cord

The Brain

Ventricles Cavities within the brain that produce and circulate CSF Lateral ventricles Third ventricle Fourth ventricle

Choroid Plexus Network of capillaries in the walls of the ventricles Covered with ependymal cells that form the cerebrospinal fluid These ependymal cells are so close together they form the blood-brain barrier. Selectively permeable barrier Protects the brain and spinal cord from potentially harmful substances in the blood

Blood Supply to the Brain One of the most metabolically active organs in the body Makes up only 2-3% of body weight but uses about 20% of available O2 at rest Well supplied with O2 and nutrients Only nutritional source for brain metabolic activity is glucose Capillaries in the brain are much less leaky than other capillaries in the body and form a blood brain barrier

Lobes of the Cerebrum Named after the bones that cover them Frontal Lobe -Temporal Lobe Parietal Lobe -Occipital Lobe 8

Frontal Lobe Motor Areas Association Areas Controls movement of voluntary skeletal muscles Association Areas Carry on high level intellectual processing Problem Solving - Reasoning - Planning Concentration - Memory - Behavior Emotions - Expressions 9

Parietal Lobe Sensory Areas Association Areas Interprets sensations such as: touch - pressure – pain Association Areas Understanding of speech Using words to express thoughts and feelings 10

Temporal Lobe Sensory Areas Association Areas Hearing and balance Interpret sensory experiences Memory of visual scenes - music - smells and other complex sensory patterns 11

Occipital Lobe Sensory Areas Association Areas Visual processing and interpretation Association Areas Combines visual images with sensory experience 12

Protection and Coverings of the Brain Protected by the cranial bones and the cranial meninges Dura Mater - outer layer Arachnoid - middle layer Pia Mater - inner layer Also protected by cerebrospinal fluid fluid that nourishes and protects the brain and spinal cord continuously circulates through the subarachnoid space around the brain and throughout the cavities within the brain

Meninges of the Brain

Meninges Connective tissue covering the brain and spinal cord Three layered membrane Dura Mater – “Tough mother” dense irregular connective tissue Arachnoid - middle layer. “Spider web” spider web arrangement of collagen fibers Pia Mater - inner most meninges very delicate layer of thin tissue

Spinal Cord Protective Coverings Dura Mater Arachnoid Pia Mater

Spinal Nerves / Brachial Plexus

Cerebrospinal Fluid Mechanical Protection Circulation Shock absorption Buoys the brain Circulation Medium for exchange of nutrients and waste products between the blood and nervous tissue

The End!

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