The Brain PDF

The Brain 0 Nervous System (NS) One of the control systems of the body (the other control system is the endocrine) the difference that the nervous system is short term, and the endocrine is long term. Nervous tissue divisions:  Anatomically (according to structure): 1. Central Nervous System (in...

The Brain 0 Nervous System (NS) One of the control systems of the body (the other control system is the endocrine) the difference that the nervous system is short term, and the endocrine is long term. Nervous tissue divisions:  Anatomically (according to structure): 1. Central Nervous System (inside bone): a) Brain (inside the cranium):superior part of the central nervous system. b) Spinal cord(inside the vertebral canal).  Tract: collection of nerve fibers inside CNS.  Nucleus: collection of neuronal cell bodies inside the CNS. 2. Peripheral Nervous System (outside bone):  The nervous cell: dendrites, axon, cell body, nerve endings.  Nerve: a collection of axons (nerve fibers) outside the CNS.  Peripheral nerves: Cranial (arise from the brain 12 pairs) & Spinal (arise from spinal cord 31 pair: 8 cervical ,12thoracic, 5 lumbar, 5 sacral, 1 coccygeal-)  Ganglia: collection of neuronal cell bodies outside the CNS.  Receptors: ex.: sensory receptors, special sensory receptors.  Physiologically or functionally the NS is divided into: 1.Somatic NS: related to the body, divided into: a) motor: voluntary, skeletal muscles (only excitatory) b) sensory: under conscious perception, divided into: 1-general: pain, touch, temp., pressure (anywhere in our body) 2- special: taste, smell, hearing, vision, equilibrium (restricted to special organs). 2.Autonomic NS (something like automatic), divided into: a) Motor: control involuntary motion, it can be excitatory or inhibitory, ex.: the stomach movement, divided into: 1- sympathetic (fight or flight): under stress, anger, cause: increasing the heart rate, increasing the respiratory rate, dilate pupil. 2- parasympathetic (rest and digest): decreasing the heart rate, decreasing the respiratory rate b) Sensory: example stretch receptor from the heart (subconscious level). Nervous System: Cell Types  Two main types of tissue: 1. Neurons: the functional unit of CNS (the smallest unit that can do the function of the organ), its function: initiate and propagate nerve impulses or action potentials. 1 2.Neuroglial cells (glia: something like glue):  Microglial cell: the macrophages of the CNS.  Astrocyte: participate in the formation of blood brain barrier(BBB).  Oligodendrocytes (like tree): wraps around the axon in process of myelination.  Ependymal cells: line cavities of the brain. The Brain The superior part of CNS that lies within the skull & continues with spinal cord through foramen magnum. Major Parts of the Brain (embryologically: the brain develops from brain vesicles)  Forebrain(prosencephalon): 1- Cerebrum: the largest part of the brain. 2- Diencephalon: Thalamus, Hypothalamus.  Midbrain (mesencephalon)  Hindbrain(rhombencephalon): Pons, Medulla oblongata, Cerebellum (cerebellum : the second large part of the brain). - Brain Stem  Not The Same as Hindbrain - Brain Stem Mid brain, Pons, Medulla Oblongata Cerebrum  Largest part of brain.  Folded appearance externally:  because it has upward projection called gyrus and downward slits(valleys) called Sulcus. Falx Cerbri & Cranial Fossae.  The purpose of the folds: during growth rapid division occur so it provides wide surface area to allow for more neurons.  the cerebrum is formed from: 2 cerebral hemispheres: (Rt. & Lf.) separated by (longitudinal fissure: deep groove)  Falx cerebri occupy the long. Fissure, it prevents rotary movement. Internal Structure of Cerebrum  Outer Layer: called the Cerebral Cortex, it’s the Gray matter, folded from outside into: gyri & sulci.  Inner Layer: - known as white matter. - Brain nucleus (nuclei): aggregation of neuronal bodies (gray matter) in white matter.  What do gray & white matters refer to? 2  Gray matter: nerve cells’ bodies (Nissl body make it dark), dendrites, unmyelinated axons.  White matter: myelinated axons (composed of fat make it white color). - The myelin has a glistening white appearance, made up of myelinated nerve fibers (axons)of different diameters supported by neuroglia.  Remember the neuronal cell: consists of: neuronal cell body, dendrites, axon, and nerve endings. Classification of Nerve Fibers of White Matter  Categorized based on their course and connections into: 1- Association fibers white matter that link different cortical areas in the same hemisphere. divided into:  Short association fibers: two adjacent areas.  Long association fibers: two apart areas. Association Fibers 2-Commissural fibers link corresponding cortical areas in the two hemispheres. Every two homologous areas connected by fibers that cross the two hemispheres.  The Largest Brain Commissure  Corpus Callosum (the hard body) located at the inf. Border of falx cerebri. 3-Projection fibers  connect the cerebral cortex with lower CNS parts, divides into: A)descending fibers (motor). B)ascending fibers (sensory). Brain Nuclei  Brain Nucleus (Nuclei): densely packed cell bodies within the CNS, the most important example: thalamus (it’s very large nucleus).  Gray matter in white matter in the PNS they are called ganglion (ganglia). External Aspect of Cerebrum  Folded into Gyri & Sulci to  surface area.  When I look at each hemisphere I can divide it into four lobes each according to the bone covering it.  Subdivided by sulci into lobes in relation to bones covering them: 1. Frontal. 2. Parietal. 3. Occipital: divided by imagenary line. 4. Temporal. Fifth cerebral lobe(insula=island) 3 Main Cerebral Sulci  Central Sulcus: separates Frontal from parietal lobes Located between 2 important gyri: Precentral gyrus in Frontal lobe (the primary motor area). Postcentral gyrus in Parietal lobe (the primary somatosensory area)  Lateral Sulcus (fissure because its deep): separates the frontal and parietal lobes from the temporal lobe.  Parieto-occipital Sulcus (imaginary line that can’t be seen laterally but it can be seen medially): separates parietal lobe from occipital lobe. - more prominent medially.  Calcarine Sulcus (in the middle of occipital lobe): Y shaped sulcus that meets the parieto-occipital sulcus anteriorly, it’s on medial surface of occipital lobe  the cortex around the Calcarine Sulcus is region of visual interpretation so hit in the occipital bone can or stroke in this area result in blindness. Precentral Gyrus  The primary motor area: controls voluntary skeletal muscle movement at the opposite side of the body.  Motor homunculus (little man): 1) Inverted: the most sup. Part of the body controlled by the most inf. Part of the brain. - Lower part  face & neck -Middle part  upper limbs. -Upper & medial parts  lower limbs. 2) Contralateral: Due to decussation (cross over) of fibers.  Large motor neurons project from precentral gyrus, down in the white matter of the brain, down to the brain stem at the lower border of medulla oblongata the great pyramidal decussation occurs. 3) Disproportional to size: -depending on skilled movements - Trunk  less brain area. - Hand & fingers  larger areas  Controls voluntary movement on opposite side of the body.  Motor control in precentral gyrus is represented in an inverted position.  Decussation of Motor Fibers, decussation of Pyramids (medulla oblongata). 4 Postcentral Gyrus  The primary sensory area. (sensory nerve cells, general sensation, and localization of sensation: determine the sense and where it is) Sensory homunculus: 1) Inverted. 2) Contralateral: fibers will cross either on the brain or in the spinal cord. 3) Disproportional to size:(depending in the number of receptors) All of the senses relay on the thalamus (Except the sense of smell).  Receives inputs for:  General sensation &localization of sensations.  General sensations: pain, temperature, touch & pressure (tickling).  Receives the sensations from opposite side of the body.  Motor & Sensory Homunculus  Disproportional to organ size.  Inverted.  Contralateral. Decussation of Sensory Fibers Main Functional Regions in Cerebrum 1.Motor area:  Location: precentral gyrus on the frontal lobe. 2.Sensory area:  Location; postcentral gyrus on the parietal lobe. 3.Auditory area:  interpretation of sound, location: in the middle of superior temporal gyrus in the temporal lobe. 4.Visual area:  location: occipital lobe area around the calcarine sulcus. 5. Motor Speech area:  (Broca’s area) speech production & comprehension.  location: In the middle of inferior frontal gyrus directly above the lateral sulcus. 6 - Sensory Speech Area (Wernicke’s area, Language’s Area): understand written and spoken language.  location: In the posterior part of the superior temporal gyrus, Posterior to: primary auditory area.  These areas (Broca’s and Wernicke’s) is located just on the dominant hemispheres( left handed personright hemisphere, right handed person left hemisphere) 5 -How we greet each other: You say hi primary auditory area on the middle of sup. Temporal gyrus  Wernicke’s area(understand what you said) Broca’s area pre central gyrus  multiple nerves send motor orders to say hi.  Associations area: the meaning of what I have hear/seen.  The prefrontal cortex responsible for the highest brain functions: thinking, decision making, social behavior. (It is affected when a person is under the influence of alcohol( Diencephalon  Hidden by cerebrum: inner part covered by cerebrum.  Consists of: Thalamus 1.Thalamus Paired oval masses of gray matter (contains many nuclei)  Usually occupies 80% of diencephalon hypothalamus  Interthalamic connection- intethalamic adhesion (massa intermedia): a bridge of gray matter joins the two halves of the thalamus (in 70% of human brains) – unknown function  The difference between Corpus callosum and massa intermedia is that Corpus callosum is white matter and massa intermedia is gray matter. Main Function of thalamus: Thalamus  a major relay station for sensory pathways (all general and special sensation must pass through the thalamus, and it will distribute them to the areas). Except  sense of smell; olfactory system will directly go the limbic system (emotional central). 2-Hypothalamus:  Below or inferior to thalamus.  A gland that secretes several neurohormones, like oxytocin and ADH and it stores them in the pituitary gland.  Contains special nerve cells that secrete several neurohormones. Main Functions: 1- Control pituitary gland secretions (ant.:(indirectly through hypothalamic hypophyseal portal system, through blood and releasing hormones) & post.:(directly through axons)) 2- Controls the autonomic NS (ANS).  Hypothalamus links  The Nervous System to the Endocrine System. Midbrain (Mesencephalon)  Superior part of brain stem, Connects forebrain to hindbrain.  Consists of:  2 halves (anteriorly): Cerebral Peduncles.  1 part posteriorly: Tectum 6  Separated by the cerebral aqueduct which is the cavity of midbrain containing CSF it divides the midbrain into: 1- Cerebral peduncles (anterior part, 2 peduncles):  Each peduncle consists of: Cerebral peduncle  Anterior Part: crus cerebri.  Posterior Part: tegmentum.  Middle part: substantia nigra: contain neurons which are dopaminergic they contain the neurotransmitter dopamine, and it gives the substance the black color function in motor movement, degeneration in these neurons lead to decrease in this neurotransmitter and lead to Parkinson’s disease (‫)شلل الرعاش‬ 2- The tectum (Posterior): 2 Superior colliculi,2 Inferior colliculi The Hindbrain(rhombencephalon)  Made up by: Pons, Medulla oblongata, Cerebellum.  The cavity of the forebrain of the cerebrum:  is known as the lateral ventricle, one cavity in each cerebral hemisphere.  the cavity of the midbrain between the masses of the thalamus is called the third ventricle.  and The cavity inside the hindbrain is known as fourth ventricle.  Pons:  Means  bridge: because it contains nerve fibers that connects the two halves o the cerebellum and it contains the ascending and descending fibers that connects the midbrain to medulla oblongata.  Cerebellum : Have two hemispheres and they are connected together by nerve fibers that pass through pons.  Middle part of brainstem located between midbrain superiorly and medulla inferiorly and Anterior to cerebellum.  Connect midbrain to hind brain.  Function: Contains bundles of axons that connect the 2 halves of cerebellum.  Medulla Oblongata  Lower part of brainstem: part of brainstem and hindbrain at the same time.  Connects  Brain to the spinal cord (it will be continuous with spinal cord at level of foramen magnum. 7  Important features:  Anterior median fissure (Deep sulcus).  2 lat. Pyramids(contain motor fibers that descend from the cerebral cortex from the motor area downward in the crus cerebri, pons, and when reach the medulla oblongata they form pyramids (that’s why it’s Prominent)  two projections lateral to ant. Median fissure: 2 olives  projections lateral to pyramids brain nuclei the olivary nucleus (the most imp. : the inf. Olivary nucleus). The brainstem  Made up by: Midbrain, Pons & Medulla oblongata.  Functions:  Conduit for the ascending. (sensory) & descending tracts(motor).  Contains important reflex centers cardiovascular center, respiratory center, swallowing reflex center, cough and sneeze reflex. Cerebellum  The second largest part of brain 1/10 of brain mass, yet ½ of neurons in the brain are located in it.  Location:  posterior to brainstem.  lies in post. Cranial fossa.  located beneath tentorium cerebelli.  Tentorium cerebelli: fold of dura mater that separates inferior aspect of cerebrum from cerebellum.  Function:  coordination of muscle tone & movements on same side of body (equilibrium and balance) like walking, writing, dancing, the learnt movements.  The process will be automatic after learnt and saved in the cerebellum.  Problem in cerebellum will result in clinical condition called: Ataxia. Ataxia  Loss of balance & loss of coordinated movement so the patient will be unable to make balanced motion.  Tend to fall to the same side of the problem if the problem was in right hemisphere patient will fall in his right side.  we have two tests for the ataxia: 8  Finger to nose test: the doctor asks the patient to hit his nose with his finger, the normal person will do this from the first time while the patient will not be able to put his finger on his nose directly.  Heel to knee test: the doctor asks the patient to put his heel on his knee, if there is a problem of the cerebellum the patient will not be able to do that from the first attempt. Work of the cerebellum:  the cerebellum will receive inputs from the precentral gyrus about the intended movement.  The proprioceptors: located in the joints and muscles send to the cerebellum about actual movement.  the cerebellum will compare between the intended movement and the actual movement, then it will correct it and send the correction to the precentral gyrus to correct any error.  so its receive from two sites:  from cerebrum the intended movement.  from muscles the actual movement. If you have any questions don’t hesitate to contact us The End 9