Structural Classification of the Nervous System

Transcription

1 Structural Classification of the Nervous System Central nervous system (CNS) Brain and spinal cord Activates nerve responses Interprets sensations Peripheral nervous system (PNS) Composed of all the nerves and their branches Spinal nerves (12 pairs) Cranial nerves (31 pairs)

2 Peripheral Nervous System Voluntary (Somatic) Travels to and from the muscles Have some control over The brain sends impulses to nerves that travel down the spinal cord. Then, nerves leave the spinal cord and travel to your muscles, telling them to contract. 2 Subsystems Autonomic We have little or no control over these nerves Examples: Heart beating Food digesting Hormones Secreting 2 parts Sympathetic and Parasympathetic

3 Parasympathetic system Nerves originate in the brain and lowest part (the sacrum) of the spinal cord. Impulses tend to slow us down. Sympathetic system Nerves spring from the chest (thoracic) and lower back (lumbar) regions of the spinal cord. Impulses tend to speed us up, becoming really activated when we are in a fight or flight situation. These are situations in which we experience a sudden threat of danger (real or imagined) to our physical or mental well-being.

4 Three Functions of the Nervous System 1. Sensory input gathering information To monitor changes occurring inside and outside the body Changes = stimuli 2. Integration -To process and interpret sensory input and decide if action is needed 3. Motor output A response to integrated stimuli The response activates muscles or glands

5 Two Functional Classification of the Peripheral Nervous System 1. Sensory (afferent) division Nerve fibers that carry information to the central nervous system 2. Motor (efferent) division Nerve fibers that carry impulses away from the central nervous system Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary

6 Nervous Tissue: Support Cells Support cells in the CNS are grouped together as neuroglia Function: to support, insulate, and protect neurons Control chemical environment of the brain. Unlike most nerve cells, neuroglia are able to replicate.

7 Astrocytes Nervous Tissue: Support Cells Abundant, star-shaped cells Brace neurons Form barrier between capillaries and neurons Control the chemical environment of the brain

8 Nervous Tissue: Support Cells Microglia Spiderlike phagocytes Dispose of debris

9 Nervous Tissue: Support Cells Ependymal cells Line cavities of the brain and spinal cord Circulate cerebrospinal fluid

10 Nervous Tissue: Support Cells Oligodendrocytes Wrap around nerve fibers in the central nervous system Produce myelin sheaths = insulation of the nerves

11 Nervous Tissue: Support Cells Satellite cells Protect neuron cell bodies Schwann cells Form myelin sheath in the peripheral nervous system

12 Nervous Tissue: Neurons Neurons = nerve cells Cells specialized to transmit messages Most neurons of the CNS can not replicate Major regions of neurons Cell body nucleus and metabolic center of the cell Processes fibers that extend from the cell body The longest process in the human body is 3 to 4 feet long. The Sciatic nerve runs from the lower back to the big toe.

13 Nervous Tissue: Neurons Processes outside the cell body Dendrites conduct impulses toward the cell body Axons conduct impulses away from the cell body Axonal terminals are separated from the next neuron by a gap Synaptic cleft gap between adjacent neurons Synapse junction between nerves

14 Neuron Cell Body Location Most neuron cell bodies are found in the central nervous system Gray matter cell bodies and unmyelinated fibers Nuclei clusters of cell bodies within the white matter of the central nervous system Ganglia collections of cell bodies outside the central nervous system

15 Functional Classification of Neurons Sensory (afferent) neurons Carry impulses from the sensory receptors to the CNS Cutaneous sense organs Proprioceptors detect stretch or tension Motor (efferent) neurons Carry impulses from the central nervous system to viscera, muscles, or glands

16 Functional Properties of Neurons Irritability Ability to respond to stimuli Conductivity Ability to transmit an impulse Action potential If the action potential (nerve impulse) starts, it is propagated over the entire axon Impulses travel faster when fibers have a myelin sheath

17 Transmission of a Signal at Synapses Impulses are able to cross the synapse to another nerve Neurotransmitter is released from a nerve s axon terminal The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter An action potential is started in the dendrite

18 Two Types of Reflexes and Regulation 1. Somatic reflexes Activation of skeletal muscles Example: When you move your hand away from a hot stove. 2. Autonomic reflexes Smooth muscle regulation Heart and blood pressure regulation Regulation of glands Digestive system regulation

19 Four Regions of the Brain 1. Cerebral hemispheres (cerebrum) 2. Diencephalon 3. Brain stem 4. Cerebellum

20 Cerebrum Cerebral Hemispheres (Cerebrum) Paired (left and right) superior parts of the brain Includes more than half of the brain mass The surface is made of ridges (gyri) and grooves (sulci) Lobes of the cerebrum Fissures (deep grooves) divide the cerebrum into lobes Surface lobes of the cerebrum Frontal lobe Parietal lobe *Occipital lobe *Temporal lobe

21 Cerebrum Specialized areas of the cerebrum Primary somatic sensory area Receives impulses from the body s sensory receptors Located in parietal lobe Primary motor area Sends impulses to skeletal muscles Located in frontal lobe Broca s area Involved in our ability to speak

22 Cerebrum Cerebral areas involved in special senses Gustatory area (taste) Visual area Auditory area Olfactory area Interpretation areas of the cerebrum Speech/language region Language comprehension region General interpretation area

23 Cerebrum Layers of the cerebrum Gray matter outer layer in the cerebral cortex composed mostly of neuron cell bodies White matter fiber tracts deep to the gray matter Corpus callosum connects hemispheres Basal nuclei islands of gray matter buried within the white matter

24 Diencephalon Sits on top of the brain stem Enclosed by the cerebral hemispheres Made of three parts Thalamus Hypothalamus Epithalamus

25 Thalamus Diencephalon The relay station for sensory impulses Transfers impulses to the correct part of the cortex for localization and interpretation Hypothalamus Under the thalamus Important autonomic nervous system center Helps regulate body temperature Controls water balance Regulates metabolism and emotions The pituitary gland is attached to the hypothalamus

26 Diencephalon Epithalamus Houses the pineal body (an endocrine gland) Forms cerebrospinal fluid

27 Regions of the Brain: Brain Stem Attaches to the spinal cord Parts of the brain stem Midbrain Pons Medulla oblongata

28 Midbrain Brain Stem Reflex centers for vision and hearing Pons The bulging center part of the brain stem Includes nuclei involved in the control of breathing Reticular Formation Involved in motor control of visceral organs Reticular activating system (RAS) plays a role in awake/sleep cycles and consciousness

29 Regions of the Brain: Brain Stem Medulla Oblongata The lowest part of the brain stem Merges into the spinal cord Contains important control centers Heart rate control Blood pressure regulation Breathing Swallowing Vomiting

30 Regions of the Brain: Cerebellum Two hemispheres with convoluted surfaces Provides involuntary coordination of body movements