Central Nervous System CNS
Brain
Spinal cord
Peripheral Nervous System PNS
Nerves outside the brain and spinal cord
- spinal nerves
- cranial nerves
Sensory (afferent) division
Part of PNS system
Nerve fibers that carry information to the central nervous system
(Part of PNS system)
Motor (efferent) division
-Nerve fibers that carry impulses away from the central nervous system.
- two subdivisions:
Somatic nervous system- voluntary
Autonomic nervous system- involuntary
(Support cells) nervous tissue
Satellite Cells
Protect neuron cell bodies
Support cells: nervous tissue
Schwann cells
Form myelin sheath in the peripheral nervous system
Nervous tissue: Neurons
Neurons= nerve cells
-Cells specialized to transmit messages
-Major regions of neurons:
•cell body- nucleus and metabolic center of the cell
• processes- fibers that extend from the cell body
Nervous tissue: neurons
Cell body
Nucleus
Large nucleolus
Dendrites
Conduct impulses toward the cell body
Axons
Conduct impulses away from the cell body
Axonal terminals
- Contain vesicles w neurotransmitters
- are separated from the next neuron by a gap
Synaptic Cleft
Gap between adjacent neurons
Synapse
Junction between nerves
Myelin sheath
Whitish fatty material covering axons
Schwann Cells
Produce myelin sheaths in jelly roll-like fashion
Nodes of Ranvier
Gaps in myelin sheath along the axon
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.
Sensory (afferent) neurons
Carry impulses from the sensory receptors to the CNS
- Cutaneous sense organs
- proprioceptors- detect stretch of tension
Motor (efferent) neurons
Carry impulses from the central nervous system to viscera, muscles, or glands.
Irritability
Ability to respond to stimuli
Conductivity
ability to transmit an impulse
Resting neuron
The plasma membrane at rest is polarized.
Fewer positive ions are inside the cell than outside the cell.
Depolarization
A stimulus depolarizes the neurons membrane.
A depolarizes membrane allows sodium to flow inside the membrane.
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.
Repolarization
Potassium ions rush out of the neuron after sodium ions rush in, which depolarizes the membrane.
The sodium potassium pump, using ATP, restores the original configuration.
Reflex
Rapid, predictable, and involuntary response to a stimulus.
Occurs over pathways called reflex arcs.
Reflex arc
Direct route from a sensory neuron, to an interneuron, to an effector.
Somatic reflexes
Activation of skeletal muscles
Autonomic reflexes
Smooth muscle regulation
Heart and blood pressure regulation
Regulation of glands
Digestive system regulation
Regions of the brain
Cerebral hemisphere (cerebrum)
Diencephalon
Brain stem
Cerebellum
Cerebral hemispheres (cerebrum)
- paired 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
Diencephalon
Sits on top of the brain stem
Enclosed by the cerebral hemispheres
Made of 3 parts: thalamus, hypothalamus, and epithalamus
Thalamus
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 temp
- controls water balance
- regulates metabolism
• an important part of the limbus system (emotions)
• the pituitary gland is attached to the hypothalamus
Epithalamus
Houses the pineal body
Includes the choroid plexus- forms cerebrospinal fluid.
Brain stem
Attaches to the spinal cord Parts of the brain stem: Midbrain Pons Medulla oblongata
Brain stem: Midbrain
Mostly composed of tracts of nerve fibers
Brain stem: pons
The bulging center part of the brain stem.
Mostly composed of fiber tracts.
Involved in the control of breathing.
Brain stem: medulla oblongata
Lowest part of the brain stem. Merged into the spinal cord. Includes important fiber tracts. Contains important control centers: Heart rate control Blood pressure regulation Breathing Swallowing Vomiting
Brain stem: Reticular formation
Diffuses mass of gray matter along the brain stem.
Involved in motor control of visceral organs.
Reticular activating system (RAS) plays a role in awake/sleep cycles and consciousness.
Regions of the brain: cerebellum
Two hemispheres with convoluted surfaces
Provides involuntary coordination of body movements.
Protection of the Central Nervous System
Scalp and skin Skull and vertebral column Meninges Cerebrospinal fluid(CSF) Blood- brain barrier
Meninges
Dura mater
- double layered external covering
-periosteum: attached to the inner surface of the skull
- meningeal layer- outer covering of the brain.
Folds inward in several areas.
Cerebrospinal Fluid (CSF)
Similar to blood plasma composition
Forms a watery cushion to protect the brain and spinal cord.
Blood-brain barrier
Includes the least permeable capillaries of the body.
Excludes many potentially harmful substances.
Useless as a barrier against some substances.
(Alcohol, nicotine, anesthesia,gases)
Concussion
Slight brain injury
No permanent brain damage*
Contusion
Nervous tissue destruction occurs.
Nervous tissue does not regenerate.
Cerebral edema
Swelling from the inflammatory response.
May compress and kill brain tissue.
Cerebrovascular Accident (CVA)
Aka stroke
The result of a ruptured blood vessel supplying a region of the brain.
Brain tissue supplied with oxygen from that blood source dies.
Loss of some functions or death may result.
Alzheimer’s disease
Progressive degenerative brain disease
Mostly seen in the elderly but can begin in early age.
Structural changes in the brain include deposits and twisted fibers within neurons.
Memory loss, irritability, confusion, hallucinations, and death.
Spinal cord
Extends from the foramen magnum of the skill to the first or second lumber vertebra.
31 pairs of spinal nerves arise from the spinal cord.
Motor subduction of the PNS
Consists only of motor nerves
Two divisions of the autonomic nervous system:
Sympathetic division
Parasympathetic division
Functions of the nervous system:
-Sensory input- gathering information To monitor changes occurring inside and outside of the body Changes=stimuli - Integration To process and interpret sensory input and decide if action is needed - Motor output A response to integrated stimuli The response activates muscles or glands