Consists of right and left hemisphere connected by the corpus callosum
Each cerebral hemisphere is composed of different lobes- frontal, temporal, parietal and occipital
Embedded in the cerebrum is the BASAL ganglia
The Frontal Lobe of the cerebrum
Influences the personality of the person
Also responsible for judgment, abstract reasoning, social behavior, language expression and motor movement.
The Temporal lobe of the Cerebrum
This part of the cerebrum controls the hearing, language comprehension, storage and recall of memories
The LIMBIC system is deeply located in the temporal lobe. This controls the basic drives such as hunger, anger, emotion and sexual drive.
The Parietal lobe of the cerebrum
This is the principal center for the reception and interpretation of Sensation
This part interprets and integrates the sensory inputs like touch, temperature and pain
It interprets size, shape, distance and texture
The occipital lobe of the cerebrum
This functions mainly to interpret visual stimuli
Speech areas in the cerebrum
1. Wernicke’s area- responsible for the sensory reception of speech.
2.Broca’s Area- responsible for the motor speech
The second largest brain region
Has also two hemispheres
Functions to maintain muscle tone, coordinate muscle movement, posture and control balance/equilibrium
If this is damaged, muscle tone decreases and fine motor movements become very clumsy
Lies inferior to the cerebrum
Continuous with the cerebrum and the spinal cord
It is composed of the midbrain, the pons and the medulla oblongata
Functions: houses the center for respiration and cardiovascular system
This connects with the cerebrum
Contains numerous ascending and descending tracts and fibers
Connects the cerebellum with the cerebrum
Houses the respiratory center and cardiovascular center
Exit points for cranial nerves 5, 6 and 7
The Medulla oblongata
The most inferior portion of the brainstem
Serves as the center for autonomic reflexes to maintain homeostasis, regulating respiratory vasomotor and cardiac functions
Serves as exit of cranial nerves 9,10,11 and 12
The thalamus and the hypothalamus
The thalamus is the relay station of all sensory stimuli towards the brain
The hypothalamus controls body temperature, appetite, water balance, pituitary secretions and sleep-wake cycle
Brain circulation: The circle of Willis
The spinal cord
A long cylindrical structure extending from the foramen magnum to the L1 in adult, L3/L4 in pedia
In the cross section of the spinal cord, we find the GRAY matter- contains neurons; and WHITE matter-consists of nerve fibers
There are 31 pairs of spinal nerves that exit the spinal cord
The spinal cord
Each spinal nerve is formed by the dorsal root (sensory) and the ventral root (motor)
Cervical segments= 8 pairs
Thoracic segments=12 pairs
Lumbar= 5 pairs
These are 3 connective tissue layers surrounding the brain and spinal cord.
1. DURA MATER- the superficial, thickest layer. The area above the dura mater is called epidural space
2. ARACHNOID- second layer, thin and wispy.
3. PIA MATER- the deepest layer, adhered to the brain and spinal cord substance
The space in between the arachnoid and pia mater is called the arachnoid space
This arachnoid space contains the cerebro-spinal fluid (CSF)
In this space, blood vessels are also found
These are CSF filled cavities in the brain
The lateral ventricle- found in the cerebrum
The third ventricle- in the center of the thalamus and hypothalamus
The fourth ventricle- located at the base of the cerebellum
This is the fluid found inside the ventricles that bathe the brain and spinal cord
Function: provides protective cushion around the CNS
Produced by the choroid plexus in the ventricles
Absorbed by the arachnoid granulations
Tracing the CSF pathway
Lateral ventricle Interventricular foramen of Monro Third ventricle Cerebral aqueduct of Sylvius fourth ventricle exits trough the median foramen of Magendie or the lateral foramen of Luscka Subarachnoid spaces in the cisterna magna, spinal cord subarachnoid space of the brain superior sagittal sinus
The cranial nerves
Are 12 pairs of nerves that exit the brain
Can be classified as
Motor mixed (sensory and motor)
The Autonomic Nervous System
The part of the peripheral nervous system that innervates cardiac muscles, smooth muscles and glands
Functionally divided into
Sympathetic Nervous System
Parasympathetic Nervous System
The SYMPATHETIC system
Originates from the T1-L2/L3 segments of the spinal cord (thoracolumbar)
Utilized by the body for FLIGHT and FIGHT response
Neurotransmitter agents are Epinephrine and Norepinephrine (coming from the adrenal gland)
Sympathetic nervous system Pupils Salivary glands Heart Bronchi of lungs Liver Stomach Small intestines Adrenal gland Kidney Large intestine Rectum Bladder Genitals T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T 1 1 T12 L1 L2 L3
Visual Acuity (Pupillary Dilation)
Smooth Muscle tone sphincters are contracted
Metabolism ↑ glucose, ↑ fatty acids
The vegetative system
Feed and Breed responses
Cranial nerves- 3, 7, 9, 10 and S2-S4
Neurotransmitter is Acetylcholine
Parasympathetic nervous system Pupils Salivary glands Heart Bronchi of lungs Liver Stomach Small intestines Large intestine Rectum Bladder Genitals
Smooth muscle tone sphincters are relaxed
The nerve cells are excitable cells
Any stimulus will change the membrane potential and cause an action potential to generate impulse transmission or action potential
The myelin sheath of the nerve cell is responsible for the SALTATORY conduction increases the nerve transmission
What is an action potential?
The synchronized opening and closing of Na + and K + gates result in the movement of electrical charges that generates a nerve impulse or action potential.
Action potentials reach the end of each neuron where these electrical signals are either transmitted directly to the next cell in the sequence via gap junctions, or are responsible for activating the release of specialized neurotransmitter chemicals.
Action potential – another name for “spike” potential or nerve impulse
Depolarization – upward oscilloscope deflection or Na + conductance is highest (hypopolarization)
All-or-None is when the action potential amplitude never varies
Repolarization – at this point, Na + conductance is falling rapidly and K + conductance has peaked.
Absolute refractory period – time of depolarization (Na + gates open)
Relative refractory period – time of depolarization (K + gates open)
Electrical synapses between excitable cells allow ions to pass directly from one cell to another, and are much faster than chemical synapses
An action potential at one node of Ranvier causes inwards currents that move down the axon, depolarizing the membrane and stimulating a new action potential at the next node of Ranvier.
What is saltatory conduction? An action potential at one node of Ranvier causes inwards currents that move down the action, depolarizing the membrane and stimulating a new action potential at the next node of Ranvier.
This is the region where communication occurs between 2 neurons or between a neuron and a target cell
A neurotransmitter is released from the nerve cell towards the other cell with receptor
Reflex Arc The reflex arc is a hard wired, unconscious rapid response to external stimulus involving spinal nerves and effector cell. A reflex is an automatic, involuntary response of an organism to a stimulus. The entire nervous system is composed of innumerable reflex arcs.
REFLEXES IN MAN
Biceps reflex & Radial-ulnar reflex
What is synaptic transmission ?
Synaptic transmission is the process by which nerve cells communicate among themselves and with muscles and glands.
The synapse is the anatomic site where this communication occurs.
Most synaptic transmission is carried out by a chemical called a neurotransmitter.
The neurotransmitter is manufactured by the neuron and stored in vesicles at the axon terminals
When the action potential reaches the axon terminal, it causes the vesicles to release the neurotransmitter molecules into the synaptic cleft.
The neurotransmitter diffuses across the cleft and binds to receptors on the post-synaptic cleft cell. Then the activated receptors cause changes in the activity of the post-synaptic neuron.
The neurotransmitter molecules are released from the receptors and diffuse back into the synaptic cleft.
The neurotransmitter is reabsorbed by the post synaptic neuron. This process is known as reuptake.
Physiology of Vision
Light waves travel at a speed of 186,000 miles per second. Light is reflected into the eyes by objects within the field of vision.
In order to achieve clear vision, light reflected from objects within the visual field is focused in to the retina of both eyes.
The processes involved in producing a clear image are refraction of the light rays and accommodation of the eyes.
The eye and the visual pathway
Vision is made possible by the stimulation of the photoreceptor cells in the retina
Receptor cells are the RODS and CONES
The eye is made up of three layers
Fibrous layer- sclerae and cornea
Uvea- choroid and iris and ciliary bodies
Nervous coat- retina
Functions of the Parts of the Eye
Lens – refraction and focusing
Iris – regulated light entrance
Pupil – opening in the iris
Choroid – absorbs stray light
Sclera – for protection
Cornea – refraction of light
Ciliary body – holds lens in place
Retina – contains receptors (rods and cones)
Rods – for black and white vision
Cones – for color vision
Optic nerve – transmits impulse
Ciliary muscle – for accommodation
The optic nerve
This is the collection of fibers from the cells in the retina
It passes through the brainstem as the optic chiasm
it will reach the occipital lobe for visual interpretation
Emmetropia is normal vision.
Parallel light rays from distant objects are in sharp focus on the retina when the ciliary muscle is completely relaxed.
This means that the eye can see all distant objects clearly, with its ciliary muscle relaxed, but to focus objects at close range it must provide various degrees of accommodation.
Myopia or nearsightedness results from an axial length of the eye that is too long for the refractive power of the eye.
In this case, the focal point is in front of the retina, thus, distant objects cannot be focused on the retina.
An object can be seen clearly if it is moved closer to the eye so that the image forms in the retina.
Hyperopia results from an axial length of the eye that is too short for the refractive power of the eye .
In this case, distant objects cannot be focused clearly because the focal point is at the back of the retina.
Astigmatism or “ghost vision” is when both far and near objects appear out of focus. This is because of the uneven diameter of the cornea (oblong-shaped). For light rays to focus precisely on the retina, the cornea usually needs to be more evenly round.
Fovea & Macula
Fovea centralis is an oval, yellowish area with a depression where there are only cone cells.
Size of the Pupils
Pupil size influences accommodation by controlling the amount of light entering the eye. In a bright light the pupils are constricted. In a dim light they are dilated.
Contraction of the circular fibers constricts the pupil, and contraction of the radiating fibers dilate it.
The size of the pupil is controlled by nerves of the ANS. Sympathetic stimulation dilates the pupils and parasympathetic stimulation causes constriction.
What is Rhodopsin?
Rhodopsin or visual purple is a photosensitive pigment present only in the rods. It is bleached by bright light and when this occurs the rods can not be stimulated.
Rhodopsin is quickly reconstituted when an adequate supply of Vit A is available.
The rate at which dark adaptation takes place is dependent upon the rate of reconstitution of rhodopsin.
PHYSIOLOGY OF HEARING
How are sounds heard?
Sound waves cause movements of the tympanic membrane and these movements are both conveyed and amplified by the middle ear ossicles (malleus, incus, and stapes).
The vibrations transmitted to the ossicles cause the foot plate of the stapes to vibrate against the oval window thereby transmitting them to the inner ear.
Thus air-borne sound waves are transferred to the fluid in the inner ear.
The Vestibular apparatus
This is the part of the ear that helps in equilibrium
Located in the inner ear
The saccule and utricle control LINEAR motion
The semicircular ducts control the Angular movement/ acceleration
Physiology of Smell
The sense of smell is perceived when odorous materials in the air are carried into the nose and stimulate the olfactory cells.
Perception of odor decreases and eventually ceases due to smell adaptation
The sense of smell may affect the appetite
The Olfactory apparatus
Stimulation from the olfactory nerves will reach the limbic system of the brain
Consists of the nose and the olfactory nerve
Primary Smell & Odor System
6 primary types of
7 Odor System
PHYSIOLOGY OF TASTE
The Gustatory apparatus
The receptor for taste are cells in the tongue group together called the taste buds
They are numerous in the vallate and fungiform papillae
The Gustatory apparatus
Basic taste modalities
Sweet- tip of the tongue
Salty- over the dorsum of the tongue
Sour- sides of the tongue
Bitter- back of the tongue
How are taste perceived ?
Taste buds which consist of small bundles of cells and nerve endings of cranial nerves (VII, IX and X).
The nerve cells are stimulated by chemical substances in solution that enter the pores.
The nerve impulses are transmitted to the thalamus then to the taste area in the cerebral cortex, one in each hemisphere, where taste is perceived.
4 fundamental sensations of taste have been described: sweet, sour, bitter and salty.