Transcript create opposite responses in the effectors

Nervous System
•One of 2 controlling and communicating systems of the
body (other is the endocrine system)
•-Sensory input - Integration - Motor output
-The two principal cell types of the nervous system are:
–Neurons
•hundreds of thousands of neurons extend axons
and make synapses all over the body with other
neurons, muscles and glands
•communicate through action potentials
•allows for short response times to changes in
homeostasis (excitable cells)
–Neuroglia
•guide developing neurons to make synapses
•provide a supportive scaffolding for developed
neurons ( a supportive cell)
Organization of the Nervous System
•Central nervous system (CNS) -BRAIN and SPINAL C.
–consists of the brain located within the skull and the
spinal cord located within the vertebral foramen
•large masses of neurons
–integration and command center of the body
–covered by meninges and surrounded by
cerebrospinal fluid
•Peripheral nervous system (PNS)
–consists of neurons that bridge the gap between the
CNS that extend to other locations in the body
•propagate APs to and away from the CNS
–the neurons are organized into nerves (bundle of
axons) and ganglions (group of cell bodies outside
the CNS)
- carries messages to and from the spinal cord
Anatomical Organization
of the Nervous System
Nerves
•Nerve
–cordlike organ of the PNS consisting of axons
enclosed by connective tissue
Connective tissue coverings include:
–Endoneurium
•loose connective tissue that surrounds each
individual axon
–Perineurium
•coarse connective tissue that bundles axons into
fascicles
–Epineurium
•tough fibrous connective tissue around a nerve
Structure of a Nerve
Functional Organization of the Nervous System
Functions of the Nervous System
-Transmit sensory information
–propagate APs to the CNS following a stimulus
which has changed a variable from its set point
•from eyes, skin, blood vessels, ears, digestive
tract, joints, muscles, lungs…
•Integration
–interpretation of sensory information by the CNS
•type, location and magnitude of stimulus
•Transmit motor information
–propagate APs from the CNS to various effector
organs throughout the body
•provides a way to respond to stimuli
Neuron Types of the Nervous System
•Sensory (afferent)
–associated with sensory receptors
–propagate APs via the PNS toward the CNS
•Interneurons
–integrate information within the CNS
–receive APs from sensory neurons and initiate APs
in motor neurons (shuttle signals thru CNS)
•Motor (efferent)
–propagate APs via the PNS away from the CNS to
effectors
Basic Function of the Nervous System
Sensory Receptors
•Structures specialized to respond to stimuli:
–nerve endings (dendrites of neurons)
–sense organs
•nerve endings combined with other tissue types to
enhance detection of a stimuli
–example: taste buds
•Mechanoreceptors
–respond to touch, pressure, stretch and itch
•Thermoreceptors
–respond to changes in temperature
•Photoreceptors
–respond to light
•Chemoreceptors
–respond to chemicals
•Nociceptors
–respond to pain
Neural Integration of the CNS
• Qualitative information (salty, pain or temperature) depends
upon which neurons are propagating APs
• Quantitative (strength) information depend on:
– the number of neurons that are firing APs
– the frequency of APs fired per neuron
Myelination of Neurons of the Nervous System
-Some neurons in the CNS are myelinated, while most
are unmyelinated
-All of the neurons in the PNS are myelinated
•Areas of the CNS that are made of myelinated neurons
are called white matter
–represent the locations of long sensory and motor
neurons
•Areas of the CNS that are made of unmyelinated
neurons are called gray matter
-represent the locations of short interneurons which
make many synapses for integration to process sensory
information and initiate motor information
Reflexes
-A rapid, predictable motor response to a stimulus
•Reflexes can be:
–simple
•involve peripheral nerves and the spinal cord
–spinal reflexes (Inborn = intrinsic = innate)
–learned (acquired)
•involve peripheral nerves and the brain
•Following a stimulus, the sensory and motor information
of a reflex follows a pathway called a reflex arc
–in many spinal reflexes, the effector is nearby the
location of the stimulus
-May involve only peripheral
nerves and spinal nerves
-May involve Higher brain
centers as well
-That is, the brain may be
informed later (after the reflex
has occurred)
Reflex Arc
•There are five components of a reflex arc
–Receptor
•respond to stimulus
–Sensory neuron
•transmits the afferent impulse to the CNS
–Integration (control) center
•region within the CNS where synapses
(processing of sensory info) occur (brain or s.cord)
–Motor neuron
•sends efferent information to an effector
–Effector
•muscle fiber or gland that responds to the efferent
impulse
•the activity of the effector depends upon the
magnitude of the stimulus
-Reflexes are to limit damage i.e.
to protect quickly
Meninges and CSF
-The meninges are 3 connective tissue membranes that
lie external to the brain and the spinal cord
–dura mater
–arachnoid mater
–pia mater
–cover and protect the CNS
–hold cerebrospinal fluid (CSF)
–prevents harmful substances from entering CSF
•The CSF is the extracellular fluid of the cells of the
nervous system
–surrounds and fills the spaces within the spinal cord
and the brain
–prevents the brain from crushing under its own
weight
•protects the CNS from trauma
Meninges- connective tissue surrounding spinal cord and brain (continuous with
each other)
1. Dura Mater - most superficial
- dense irregular connective tissue
2. Arachnoid - middle layer
-avascular (no blood vessels)
- spider web arrangement of delicate collagen fibers and some
elastic
3. Pia Mater - thin transparent connective tissue that adheres to surface of
brain or spinal cord
- interlacing bundles of collagen and fine elastic fibers
- contains many blood vessels to supply oxygen and nutrients
Meninges
Brain
Cerebrum
- largest portion of the brain, about 2/3
-upper most portion and divided into 2 hemispheres
Cerebral cortex
-Outermost portion of cerebrum
-human cerebral cortex is more developed than in any other animal
• 4 lobes
– frontal, parietal, temporal and occipital
– location of interneurons for perception of all senses
– Site of memory, emotion, learning
– site of initiation of voluntary skeletal muscle contraction
•
•
•
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-superficial is called gray matter
40% of brain mass
-enables sensaton, communcation. Memory, understanding
Hemispheres are contralateral i.e. left side of brain controls
left side of face but right side of body
• -no functional area acts alone i.e. behavior
involves entire cortex
The Cerebellum
-Located dorsal to the pons and medulla
-Protrudes under the occipital lobes of the cerebrum
-Makes up 11% of the brain’s mass
•Modifies the motor information leaving the motor cortex
–provides precise timing and appropriate patterns of
skeletal muscle contraction to maintain balance and
coordination
Cerebellar activity occurs subconsciously
Responsible for balance and coordination
Brain Stem
-Comprised of the pons and the medulla oblongata
-Clusters of neurons (brain centers) in regions of the
pons and medulla control the basic life functions:
–heart rate
•controlled by the cardioacceleratory and
cardioinhibitory centers in the medulla
–blood pressure
•controlled by the cardioacceleratory,
cardioinhibitory, and vasomotor centers in the
medulla
–breathing rate
•controlled by the inspiratory and expiratory
centers in the medulla and pons, respectively
•Control of effectors occurs through the Autonomic
Nervous System
•Provides pathways between higher and lower brain
centers
Brain
Hypothalamus and Pituitary
•Hypothalamus and Pituitary (Master glands) (caps Brain
stem)
–2 glands located inferior to the thalamus
–Secrete hormones which regulate a large number of
metabolic processes
•metabolic rate
•sex hormone levels in the blood
•growth
•water balance
•blood nutrient levels
-The hypothalamus secretes hormones which in turn
cause the pituitary to secrete hormones, thus the
hypothalamus controls the function of the pituitary
Hypothalmus regulates blood
pressure, heart rate, force of heart
rate, rate of breathing
Perception of pleasure, maintains
body temperature
Feelings of hunger and regulates
sleep
Spinal Cord
•The spinal cord is attached to the brain and extends to
the lumbar region of the vertebral column
•Functions include:
–integration of basic stimuli presented to the body
below the neck through simple reflexes
•withdrawal reflex in response to pain
-sending sensory and motor information to and from
the brain
31 pairs of spinal nerves.
There are enlargements in the
cervical and lumbar regions where
nerves of limbs emerge.
Cauda equina is a collection of
nerve roots at the inferior end of
the vertebral column
Spinal Cord Anatomy
•Dorsal (posterior) horns (left and right)
–sensory information enter the cord on the dorsal
aspect where they synapse with interneurons or
motor neurons
-extend into dorsal roots and ganglia
•Ventral (anterior) horns (left and right)
–motor information exits the cord on the ventral
aspect where they control effectors (muscle or
glands)
-extend into motor roots
-Dorsal and ventral roots merge together to form spinal
nerves
Spinal Cord Anatomy
Peripheral Nervous System (nerves
outside of the CNS)
•The PNS consists of 12 pairs (left and right) of cranial
nerves originate from the brain and 31 pairs (left and
right) of nerves are attached to the spinal cord
•Sensory (afferent)
–all axons carry impulses from sensory receptors via
the PNS to the CNS
•Motor (efferent)
–all axons carry impulses via the PNS from CNS
•Mixed
–a mixture of sensory and motor neurons that carry
impulses via the PNS to and from CNS
– most common type of nerve in the body
Sensory Division of the PNS
Sensory division
•made of afferent neurons
–Somatic (body)
–sensory neurons send APs from skin, skeletal
muscles, and joints
–visceral sensory neurons send APs from organs
within the abdominal and thoracic cavaties
Motor Division of the PNS
Motor division
•made of efferent neurons
•control the action of effectors
–somatic motor neurons send APs to voluntary
skeletal muscle
–visceral motor neurons send APs to involuntary
cardiac muscle, smooth muscle and glands
–a.k.a. the Autonomic Nervous System (ANS)
–2 antagonistic (opposing) divisions
•Sympathetic
•Parasympathetic
–the two divisions control the same effectors
(with few exceptions) but create opposite
responses in the effectors
Autonomic Nervous System
-Visceral motor neurons of the PNS control the activity of
involuntary effectors such as cardiac muscle, smooth
muscle and glandular secretion affecting:
–heart rate
–breathing rate
–sweating
–digestion
–blood pressure
-Action potentials in these motor neurons are initiated in
the medulla oblongata and the pons
–these motor neurons exit the brain by:
•descending tracts of the spinal cord
–exit spinal cord via spinal nerves
•cranial nerves
Efferent Pathways of the ANS
-Efferent pathways of the ANS consist of a two-neuron
chain between the brain or spinal cord and the effector
-synapses between the neurons occur at ganglions
-The preganglionic begins in the CNS and extends
along a nerve to the ganglion
–The postganglionic neuron extends from the
ganglion to an effector organ
Organization of
the Sympathetic
Division
Organization of the
Parasympathetic
Division
Function of the Sympathetic Division
-The sympathetic division is called the “fight or flight”
system (mobilizes body in extreme situations)
-activated when the body needs to expend energy
•Involves E activities
•exercise, excitement, emergency, and embarrassment
•Promotes necessary changes during these activities
–increases heart rate, blood pressure, respiration
rate, blood flow to skeletal muscles, glucose
metabolism
-decreases the activity of and blood flow to the
digestive system organs
-Its activity is illustrated by a person who is threatened
-the individual’s heart rate
increases and the breathing
becomes deep
-skin is cold and sweaty
-pupils dilate
Function of the Parasympathetic Division
•The parasympathetic nervous system is called the “rest
and digest” system
–activated when the body needs to conserve energy
•Involves the D activities
–digestion, defecation, and diuresis (urination)
•Promotes necessary changes during these activities
–decreases heart rate, blood pressure, respiration
rate, blood flow to skeletal muscles, glucose
metabolism
–increases the activity of and blood flow to the
digestive system organs
Its activity is illustrated in a person who relaxes after
eating a meal
-Therefore maintenance activities
-gastrointestinal activity is high
-skin is warm and pupils
constricted
-most visceral organs are innervated by both
sympathetic and parasympathetic nerves
-Therefore, dynamic antagonisms that
precisely control visceral activity
e.g. sympathetic increases heart rate,
respiration, and inhibits digestion while the
parasympathetic decreases heart and
respiratory rates and allows for digestive
system to be rid of wastes
Neurotransmitters of Sympathetic and
Parasympathetic Divisions
•The way the 2 divisions of the ANS can create opposite
responses in the effectors that they control is by the
release of different neurotransmitters onto the cells of
the effectors
•All preganglionic neurons (sympathetic and
parasympathetic) exocytose acetylcholine (ACh) onto
postganglionic cells
–creating an AP in the postganglionic cell
•Sympathetic postganglionic cells release
norepinephrine (NE) onto the effector
•Parasympathetic postganglionic fibers release ACh onto
effector
Efferent Sympathetic vs. Parasympathetic
Effects of Neurotransmitters of the Autonomic
Nervous System
•The cells of each organ controlled by the ANS have
membrane receptors to BOTH ACh and NE
–organs are dually controlled
-The response of the organ is determined by the identity
of the neurotransmitter released
–the binding of ACh to its receptor will cause the
effector to respond in one way
-the binding of NE to its receptor will cause the
effector to respond in the opposite way
•The effect of ACh and NE on an effector can be either
stimulatory or inhibitory (effector specific)
-NE increases heart rate, ACh decreases heart rate
–NE decreases the secretion of saliva, ACh increases
the secretion of saliva
Dual Control by the
Sympathetic and
Parasympathetic Systems
Brain
Left Brain-Logic Details Facts Words
Knowing Reality
Present/past Math/Science
Right Brain- Feeling Big Picture Imagination Symbols Future
Philosophy/Religion Spatial perception Risk Fantasy
Brain Dysfunctions
Traumatic Brain Injuries
-Damage is caused not only at the site of a blow, but also by the effect of
Ricocheting brain hitting the opposite side of the skull
1. Concussion
- slight brain injury
- maybe dizzy “seeing stars” or loss of consciousness, briefly
Levels of injury:
G-1: less than 15 min
G-2: greater than 15 min
G-3: loss of consciousness
Recovery (from sport):
G-1: 1 week
G-2: 2 weeks
G-3: 1 month
2. Contusion
- marked tissue damage
- if cerebral cortex is injured the individual may remain conscious
- but severe brain stem contusions always result in a coma lasting hours
to a Lifetime
3. Inter Cranial Hemorrhage
- bleeding from ruptured vessels or cerebral edema (swelling of the
brain due to inflammatory response to injury)
- individuals who are initially alert and lucid may begin to deteriortae
neurologically later
Signs of a serious impact:
- headache that gets worse
-Confusion
-Disorientation
-Slurred speech
-Sleepiness
-Droopy eye
-amnesia
4. Cerebrovascular accident (strokes)
-3rd leading cause of death in the US
- blood circulating to the brain area is blocked (clot or ruptured blood
vessel) - vital tissues dies
- brain area affected determined by observing patient’s symptoms
5. Cerebral Palsy
-One cause: temporary lack of oxygen at birth
- neuromuscular disability => voluntary muscles are poorly controlled
because of brain damage
- 50% of patients have seizures
-some have mental retardation
- some have vision or hearing problems
Tracking down the problems:
1. Test reflexes - test of brain and spinal cord
2. Electroencephalography (EEG)
-electrodes placed on scalp to measure brain activity (impulses or brain
waves)
- patterns vary depending on activity e.g. sleeping, coma
- lack of waves means brain death
3. CT Scan - 3D image from x-rays and the use if intravenously
administered contrast dyes (high radiation)
4. MRI - Magnetic Resonance Imaging
-better image than a CT Scan
- uses a magnetic field therefore no radiation
5. PET - Positron Emission Tomography
-3D image
-uses gamma rays from a radioisotope that has a short half life
- may be used in conjunction with a CT Scan