Nervous System
Chapter 9
Introduction to the NS Neurons – nerve cells Nerve impulses – electrochemical
changes which transmit information Neurons consist of:
• Cell body – rounded area• Dendrites – extensions that receive nerve
impulses• Axons – extensions that send nerve impulses
(usually has only one) Nerves – bundles of axons Neuroglial cells – provide physical
support, insulation, and nutrients for neurons
Groups
Central nervous system – consists of brain and spinal cord
Peripheral nervous system – consists of nerves that connect the cns to the other body parts
Functions:• Sensory• Integrative• Motor
Sensory Function
Sensory receptors are found at the ends of peripheral neurons gather info. by detecting changes inside and outside the body.
Monitor such things as light, sound, temperature, oxygen level
Integrative Function
Nerve impulses from sensory receptors are transmitted to the cns
Signals are brought together, creating sensations, adding to memory, or helping produce thoughts that translate sensations into perceptions
Motor Function
Impulses from cns to responsive structures called effectors • Examples: muscles that contract, glands
that secrete Somatic nervous system – motor
functions that are consciously controlled
Autonomic nervous system – motor functions that are involuntary
Dimethylmercury Poisoning
Clings to brain neurons, destroying them
Neuroglial cells overgrow
Neuroglial Cells Microglial – scattered throughout cns; support
neurons and phagocytize bacterial cells and cellular debris
Oligodendrocytes – align along nerve fibers; provide insulating layers of myelin around axons within the cns
Astrocytes – found between neurons and blood vessels; provide structural support; help regulate conc. of nutrients and ions within the tissue; form scar tissue
Ependymal cells – form an epithelia-like membrane that covers specialized brain parts; forms inner linings
Schwann cells – form a myelin sheath around axons of the pns
Gliomas
Fast-growing brain tumors Consist of rapidly dividing neuroglia
Neurons Cell body
• Granular cytoplasm• Cell membrane• Organelles (mitochondria, lysosomes, neurofibrils)• Nissl bodies (similar to rough ER)
Dendrites• Short and highly branched• Main receptive surfaces
Axons• Conducts nerve impulses away from the cell body• Usually a single structure• Surrounded by Schwann cells to form a myelin sheath• Spaces in between are called nodes of Ranvier
Neural stem cells found in the hippocampus
Structural Classification of Neurons
Multipolar – one axon; many dendrites; lie within the brain or spinal cord
Bipolar – one axon; one dendrite; lie within eye, nose, and ears
Unipolar – one axon that branches into two; one assoc. with peripheral body part and the other enters the brain or spinal cord
Functional Classification of Neurons
Sensory neurons – carry nerve impulses from peripheral body parts into the brain or spinal cord
Interneurons – transmit impulses from one part of the brain or spinal cord to another
Motor neurons – carry nerve impulses out of the brain or spinal cord to effectors
Cell Membrane Potential
Surface of a cell membrane is usually electrically charged or polarized with respect to the inside
Polarization due to an unequal distribution of positive and negative ions between sides of the membrane
Distribution of Ions
Greater conc. of Na+ outside cell Greater conc. of K+ inside cell
Resting Potential of Neuron Resting membrane
more permeable to K+ than to Na+
K+ leaves faster than Na+ enters
There exists a potential difference of charges in a resting nerve cell between the region inside the membrane and outside the membrane
Potential Changes
Depolarization – resting potential decrease (inside becomes less negative than outside as Na ions leave)
This produces a local current If additional stimulation arrives before the
effect of the previous stimulation subsides, the change in potential is still greater (summation)
Threshold potential is reached as a result of summated potentials
Action Potential
At the threshold potential, permeability suddenly changes at the trigger zone (portion of axon where impulse begins) allowing Na+ in
Cell becomes depolarized and repolarized as K+ enter once more
Action potential – rapid sequence of depolarization and repolarization
Agh!
Local anesthetic drugs decrease membrane permeability to sodium ions
It interrupts impulses from passing through the affected region and reaching the brain
Prevents the sensations of touch and pain
Impulse Conduction
Myelinated sheath prevents almost all ion flow through the membrane it encloses
Nodes of Ranvier between Schwann cells interrupt the sheath
Action potentials occur at these nodes Speed of nerve impulse conduction is
proportional to the diameter of the axon (greater diameter=faster impulse)
All-Or-None Response
If a neuron responds at all, it responds completely
Conduction occurs when a stimulus of threshold intensity or above is applied
All impulses carried on that axon are of the same strength
Greater intensity=more impulses per second
Events leading to the conduction of a nerve impulse
1. Neuron membrane maintains resting potential
2. Threshold stimulus is received3. Sodium channels in the trigger zone
of the neuron open4. Sodium ions diffuse inward,
depolarizing the membrane5. Potassium channels in the
membrane open
6. Potassium ions diffuse outward, repolarizing the membrane
7. The resulting action potential causes a local bioelectric current that stimulates adjacent portions of the membrane
8. A wave of action potentials travels the length of the axon as a nerve impulse
Flipbook
Create a flipbook illustrating and describing the events leading to the conduction of a nerve impulse
Must be labeled, colored, and include a short description
The Synapse
Nerve impulses travel along nerve pathways
The junction between any two communicating neurons is called a synapse
Types of Nerves
Afferent fibers bring sensory information into the CNS
Efferent fibers carry impulses from the CNS to effectors (muscles or glands)
Reflex Arc Type of nerve pathway Reflexes are automatic subconscious
responses to stimuli within or outside the body
Help maintain homeostasis by controlling heart rate, breathing rate, blood pressure, and digestion
Knee-jerk reflex helps maintain upright posture
Withdrawal reflex occurs when a person unexpectedly touches a body part to something painful
Meninges
Membranes that lie between bone and soft tissues of CNS
Dura mater • outermost layer• composed of tough, white, fibrous
connective tissue• contains many blood vessels and nerves
Arachnoid mater• thin, weblike membrane• Lacks blood vessels• Lies between the dura and pia maters• Spreads over the brain and spinal cord
Pia mater• Very thin• Contains blood vessels that nourish underlying
cells of the brain and spinal cord• Hugs the surfaces of organs
Spinal Cord
Slender nerve column that passes downward from the brain into the vertebral column
Consists of 31 segments, each of which gives rise to a pair of spinal nerves
Conducts nerve impulses Serves as a center for spinal reflexes
Brain
Composed of about 100 billion multipolar neurons
Weighs about 3.5 lbs.
If all the cells were laid end-to-end, they would cover 600 miles
Cerebrum
Consists of left and right hemispheres
Deep bridge of nerve fibers called the corpus callosum connects the cerebral hemispheres
A layer of dura mater separates them Gyri – ridges found on surface Sulcus – shallow groove Fissure – deep groove
Lobes of Cerebrum
Frontal – forms anterior portion of each hemisphere
Parietal – posterior to the frontal lobe
Temporal – lies below frontal and parietal lobes
Occipital – forms posterior portion of each hemisphere
Cerebrum cont.
Cerebral cortex – outermost portion of the cerebrum composed of a thin layer of gray matter
Just beneath the cerebral cortex is a mass of white matter that makes up the bulk of the cerebrum
Provides higher brain functions Stores information that comprises
memory and utilizes it to reason
Functions of the Cerebrum
1. Motor area for voluntary muscle control
2. Motor speech area3. Auditory area4. Cutaneous sensory area5. General interpretative area6. Visual area
Hemisphere Dominance
Both hemispheres participate in basic functions
In most persons, however, one side of the cerebrum is the dominant hemisphere, controlling the ability to use and understand language
Left hemisphere is dominant in more than 90% of the population
Non-dominant hemisphere controls emotional and intuitive thinking
Cerebrospinal Fluid
Secreted by choroid plexuses found in the pia mater
Completely surrounds the brain and spinal cord
Organs float Support and protection is provided by
absorption of forces
Diencephalon
Located between the cerebral hemispheres and above the midbrain
Composed largely of gray matter Thalamus within the diencephalon relays
sensory impulses from other parts of the nervous system to the cerebral cortex
Hypothalamus lies below the thalamus and maintains homeostasis by regulating a variety of visceral activities and by linking the nervous and endocrine systems
Brainstem – bundle of nervous tissue that connects the cerebrum to the spinal cord• Midbrain – contains bundles of myelinated
axons that join lower parts of the brainstem and spinal cord with higher parts of the brain
• Pons – rounded bulge on the underside of the brainstem; relays impulses to and from the medulla oblongata
• Medulla oblongata – relays impulses, controls vital visceral activities, and reflexes
Cerebellum
Large mass of tissue located below the occipital lobes of the cerebrum and posterior to the pons and medulla oblongata
Consists of two lateral hemispheres Reflex center for integrating sensory
information concerning the position of body parts and for coordinating complex skeletal muscle movements
Helps maintain posture
Peripheral Nervous System (PNS)
Consists of nerves that branch out from the CNS and connect it to other body parts
Subdivided into the somatic and autonomic nervous systems
Somatic Nervous System
Cranial and spinal nerves Connect the CNS to the skin and
skeletal muscles Oversees conscious activities
Cranial Nerves
Autonomic Nervous System
Functions independently and continuously without conscious effort
Regulates the actions of smooth muscles, cardiac muscles, and glands
Responds to emotional stress and prepares the body to meet the demands of strenuous physical activity
Pictionary!!!
Choose a card from the deck. Draw a picture on the board for your team members to guess before time runs out. You will have one minute to complete your drawing and have your team guess before the chance goes to the other team. You may not use hand motions or any sound effects.
Disorders/Diseases
Attention Deficit-Hyperactivity Disorder • affects 3-5 percent of all American
children • interferes with a person's ability to stay
on a task and to exercise age-appropriate inhibition
• causes
Alzheimer's disease • age-related, non-reversible brain disorder that
develops over a period of years • Symptoms
behavior and personality changes decline in cognitive abilities such as decision-making
and language skills problems recognizing family and friends ultimately leads to a severe loss of mental function
and death• Cause
Plaques caused by protein buildup
Dementia• impaired intellectual functioning that interferes
with normal activities and relationships • lose their ability to solve problems and
maintain emotional control, and they may experience personality changes and behavioral problems, such as agitation, delusions, and hallucinations
• Caused by Alzheimer’s disease, vascular dementia, Lewy body dementia, frontotemporal dementia, Huntington’s disease, and Creutzfeldt-Jakob disease
Coma• profound or deep state of unconsciousness • may occur as a complication of an underlying
illness, or as a result of injuries, such as head trauma
• Although individuals in a persistent vegetative state may appear somewhat normal, they do not speak and they are unable to respond to commands
• rarely lasts more than 2 to 4 weeks
Meningitis and Encephalitis• inflammatory diseases of the
membranes that surround the brain and spinal cord and are caused by bacterial or viral infections
• sudden fever, headache, vomiting, heightened sensitivity to light, stiff neck and back, confusion and impaired judgment, drowsiness, weak muscles, a clumsy and unsteady gait, and irritability
Epilepsy• clusters of neurons in the brain
sometimes signal abnormally• strange sensations, emotions, and
behavior or sometimes convulsions, muscle spasms, and loss of consciousness
• Illness, brain damage or abnormal brain development can lead to seizures
Parkinson's Disease• result of the loss of dopamine-producing
brain cells• tremor, or trembling in hands, arms,
legs, jaw, and face; rigidity, or stiffness of the limbs and trunk; bradykinesia, or slowness of movement; and postural instability, or impaired balance and coordination