nervous system
It is composed of the brain, the spinal cord and enormous network of nerves that thread throughout the body.
nervous system
Basic Functions of the Nervous System
1.Sensation
gathering information
To monitor changes occurring inside and outside the body
Such changes are known as stimuli and the cells that monitor them are receptors.
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
Two Main Division of Nervous System
1. Central nervous system (CNS)
2. Peripheral nervous system (PNS)
Brain
Spinal cord
1. Central nervous system (CNS)
Nerve outside the brain and spinal cord (e.g. spinal nerves, cranial nerves)
Responsible for communication between the CNS and the rest of the body.
2. Peripheral nervous system (PNS)
The Peripheral nervous system (PNS) can be divided into (2):
1. Sensory (afferent) Division
2. Motor (efferent) Division
Conducts impulses from receptors to the CNS
Sensory nerve fibers can be somatic (from skin, skeletal muscles or joints) or visceral (from organs w/i the ventral body cavity)
1. Sensory (afferent) Division
Nerve fibers that carry impulses away from the CNS
2. Motor (efferent) Division
The Autonomic Nervous System can be divided into:
1. Sympathetic Nervous System
2. Parasympathetic Nervous System
Responsible for our “Fight or Flight” reactions such as
Increased Heart Rate
Increased Blood Pressure
Pupil Dilation
Decreased Urination
Increased Sweating
Bronchial Dilation
Decreased Salivation
Penile ejaculation
1. Sympathetic Nervous System
Activated during “Rest and Digestion” such as
Decreased Heart Rate
Decreased Blood Pressure
Pupil Constriction
Increased Urination
Decreased Sweating
Bronchial Constriction
Increased Salivation
Increased GI secretions and peristalsis
Penile erection
2. Parasympathetic Nervous System
- The nervous system is an organ system containing a network of specialized cells called _______
- Therefore a ______ is the functional and structural unit of the nervous system
NEURON
Major regions of neurons
1. Cell body – nucleus and metabolic center of the cell
2. Processes – fibers that extend from the cell body (dendrites and axons)
– conduct impulses toward the cell body
Dendrites
– conduct impulses away from the cell body (only 1!)
Axons
– The specialized glial cells that wrap around the axon of neurons. This is made by:
Within the CNS _____________
Within the PNS __________
1. Myelin Sheath
- Oligodendrocytes
- Schwann Cells
– the gaps in myelin sheath along the axon
Nodes of Ranvier
increase the speed of nerve conduction
Myelinization
– composed of non-myelinated fibers and cell bodies
Grey Matter
– composed of Myelinated neurons
oBrain – Grey matter covers white matter
oSpinal Cord – White matter covers grey matter
White Matter
Functional Classification of Neurons
1. Sensory (afferent) neurons
2. Motor (efferent) neurons
3. Interneurons (association neurons)
Carry impulses from the sensory receptors to CNS ( e.g. Cutaneous sense organs, Proprioceptors – detect stretch or tension)
1. Sensory (afferent) neurons
Carry impulses away from the CNS to the effector organ (e.g muscles)
2. Motor (efferent) neurons
Found in neural pathways in the central nervous system
Connect sensory and motor neurons
3. Interneurons (association neurons)
Characteristics of a Neuron
1. Irritability – ability to respond to stimuli
2. Conductivity – ability to transmit an impulse
The plasma membrane at rest is polarized (Fewer positive ions are inside than outside the cell membrane )
Starting a Nerve Impulse
– a stimulus depolarizes the neuron’s membrane
A depolarized membrane allows sodium (Na+) to flow inside the membrane (Na influx)
The exchange of ions initiates an action potential in the neuron
Depolarization
-The largest division of the brain (more than half of the brain mass). It is divided into two hemispheres (left and right), each of which is divided into four lobes.
Frontal
Parietal
Occipital
Temporal
Cerebral Hemispheres (Cerebrum)
- The outermost layer of gray matter making up the superficial aspect of the cerebrum.
Cerebral Cortex
Cerebral Features:
•Gyri (Gyrus: singular)
•Sulci (Sulcus: singular)
- Central Sulcus
•Fissures
- Longitudinal Fissure –
- Transverse Fissure –
- Sylvian/Lateral Fissure
– Elevated ridges “winding” around the brain.
Gyri (Gyrus: singular)
– Small grooves dividing the gyri
•Sulci (Sulcus: singular)
– Divides the Frontal Lobe from the Parietal Lobe
•Central Sulcus
– Deep grooves, generally dividing large regions/lobes of the brain
•Fissures
– Divides the two Cerebral Hemispheres
•Longitudinal Fissure
– Separates the Cerebrum from the Cerebellum
•Transverse Fissure
– Divides the Temporal Lobe from the Frontal and Parietal Lobes
•Sylvian/Lateral Fissure
• located deep to the Frontal Bone of the skull.
• It plays an integral role in the following functions/actions:
-Memory Formation
-Emotions
-Decision making/reasoning
-Personality
1.Frontal lobe
Frontal Lobe - Cortical Regions
•Primary Motor Cortex (Precentral Gyrus)
•Broca’s Area
- Broca’s Aphasia
– Cortical site involved with controlling movements of the body.
•Primary Motor Cortex (Precentral Gyrus)
– Controls facial neurons, speech, and language comprehension. Located on Left Frontal Lobe.
•Broca’s Area
– Results in the ability to comprehend speech, but the decreased motor ability (or inability) to speak and form words.
•Broca’s Aphasia
• located deep to the Parietal Bone of the skull.
• It plays a major role in the following functions/actions:
- Senses and integrates sensation(s)
-Spatial awareness and perception
(Proprioception - Awareness of body/ body parts in space and in relation to each other)
2.Parietal Lobe
- Awareness of body/ body parts in space and in relation to each other)
Proprioception
Parietal Lobe - Cortical Regions
•Primary Somatosensory Cortex (Postcentral Gyrus)
•Somatosensory Association Cortex
• Primary Gustatory Cortex
– Site involved with processing of tactile and proprioceptive information.
•Primary Somatosensory Cortex (Postcentral Gyrus)
- Assists with the integration and interpretation of sensations relative to body position and orientation in space. May assist with visuo-motor coordination.
•Somatosensory Association Cortex
– Primary site involved with the interpretation of the sensation of Taste.
• Primary Gustatory Cortex
• located deep to the Occipital Bone of the Skull.
• Its primary function is the processing, integration, interpretation, etc. of VISION and visual stimuli.
3.Occipital Lobe
occipital lobe- caortical region
•Primary Visual Cortex
• Visual Association Area
– This is the primary area of the brain responsible for sight -recognition of size, color, light, motion, dimensions, etc.
•Primary Visual Cortex
– Interprets information acquired through the primary visual cortex.
• Visual Association Area
•located on the sides of the brain, deep to the Temporal Bones of the skull.
•They play an integral role in the following functions:
•Hearing
•Organization/Comprehension of language
•Information Retrieval (Memory and Memory Formation)
4.Temporal Lobe
Temporal Lobe – Cortical Regions
•Primary Auditory Cortex
• Primary Olfactory Cortex
•Wernicke’s Area
- Wernicke’s Aphasia
– Responsible for hearing
•Primary Auditory Cortex
– Interprets the sense of smell once it reaches the cortex via the olfactory bulbs. (Not visible on the superficial cortex)
• Primary Olfactory Cortex
– Language comprehension. Located on the Left Temporal Lobe.
•Wernicke’s Area
– Language comprehension is inhibited. Words and sentences are not clearly understood, and sentence formation may be inhibited or non-sensical.
Wernicke’s Aphasia
- is a language disorder that affects the ability to understand and produce meaningful speech. It is caused by damage to the Wernicke's area in the brain, which is responsible for language comprehension. An example of _________ is the sentence: 'The thing ate space after exploding by the pool.' In this sentence, the words are nonsensical and do not convey a clear meaning, which is a characteristic of _________-.
Wernicke's aphasia
- A white matter tract that connects Broca’s Area and Wernicke’s Area through the Temporal, Parietal and Frontal Lobes. Allows for coordinated, comprehensible speech. Damage may result in: - Conduction Aphasia
Arcuate Fasciculus
- Where auditory comprehension and speech articulation are preserved, but people find it difficult to repeat heard speech.
- Conduction Aphasia
Attaches to the spinal cord
Parts of the brain stem
Midbrain
Pons
Medulla oblongata
The Brain Stem
-Mostly composed of tracts of nerve fibers
Reflex centers for vision and hearing
Cerebral aquaduct – 3rd-4th ventricles
1. The midbrain
The bulging center part of the brain stem
Mostly composed of fiber tracts
Includes nuclei involved in the control of breathing
2.Pons
oThe lowest part of the brain stem
oMerges into the spinal cord
oIncludes important fiber tracts
oContains important control centers
-Heart rate control
-Blood pressure regulation
-Breathing
-Swallowing
-Vomiting
3.Medulla Oblongata
Composed of two hemispheres with convoluted surfaces below the cerebrum
Provides involuntary coordination of body movements
The Cerebellum
Protection of the Central Nervous System
Scalp and skin
Skull and vertebral column
Meninges
Cerebrospinal fluid
The Meninges
1.Dura matter
2.Arachnoid layer
3.Pia mater
Double-layered external covering
Periosteum – attached to surface of the skull
Meningeal layer – outer covering of the brain
1.Dura matter
a.Middle layer of the meninges
2.Arachnoid layer
a.Internal layer
b.Clings to the surface of the brain
3.Pia mater
The space between the arachnoid and the pia matter __________ is filled with Cerebspinal fluid
(subarachnoid space)
Similar to blood plasma composition (hence, has been regarded as an ultrafiltrate of the blood plasma)
In a man the total volume of CSF has been estimated to be about 140 ml
Formed by the choroid plexus
Forms a watery cushion to protect the brain
Circulated in arachnoid space, ventricles, and central canal of the spinal cord
The Cerebrospinal Fluid
A long cylindrical structure invested by meninges, which lies in the vertebral canal.
Extends from foramen magnum (opening at the base of the skull) to the region of between L1 and L2
31 spinal nerves sprout from the spinal cords
8 cervical nerves
12 thoracic nerves
5 lumbar nerves
5 sacral nerves
1 coccygeal nerve
The Spinal Cord
= bundle of neuron fibers
Neuron fibers are bundled by connective tissue
Nerve