Central Nervous System (CNS) -> brain and spinal cord Major Divisions of the nervous system: Afferent (sensory input) -> cell bodies outside of the central nervous system (CNS), carry info into the CNS Efferent (motor output) -> cell bodies inside the CNS, motor or effector neurons that carry nerve impulses away from the central nervous system to effectors such as muscles or glands (and also the ciliated cells of the inner ear) Cranial Nerves -> nerves that directly emerge from or lead to the brain and brain stem, related to somatic, visual, olfactory (smell), taste and auditory senses. Spinal Nerves -> emerge from the spinal cord, related to somatic sensation (touch, temperature, pain) Visceral -> somatic sensation in the gut, stomach and insides Autonomic efferent -> involuntary decision, carries info from CNS to stimulate for example; smooth & cardiac muscles Somatic efferent -> voluntary decision, carries info from CNS to stimulate the skeletal muscles Brain Anatomy:
Having wrinkles on the brain increases its surface area Sulcus -> grooves in the brain (valley) Gyrus -> part that sticks out (hill) Cerebellum -> smaller portion of brain below the Cerebral cortex Cerebrum Cortex -> the larger portion of the brain 4 main lobes of the Brain: 1. Frontal lobe -> most front part, responsible for reasoning, motor skills, language & higher level of cognition, near the central sulcus is the motor cortex 2. Parietal lobe -> central lobe, contains the somatosensory cortex which helps with the processing of the senses 3. Occipital lobe -> the lobe in the back, helps process information from visual stimuli, the location of the primary visual cortex 4. Temporal lobe -> lobe at the bottom section of brain, location of the auditory cortex so helps process information related to sound, also contains the hippocampus so it's also centre for memories. Central sulcus -> separates the frontal and parietal lobe Lateral sulcus -> divides the temporal lobe from the frontal and parietal lobes. Corpus callosum -> it's a bundle of nerves that connects the two hemispheres (left and the right) of the brain and facilitates the communication between them Thalamus -> relay centre for sensory and motor signals in the brain Brainstem -> 3 parts to it: Midbrain, Pons and Medulla
Midbrain -> associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation Pons -> helps transmit information Medulla -> helps perform involuntary functions of the body (regulation, breathing) Spinal Cord -> transmits information from the brain to the rest of the body Coronal slice/plane -> cut in half from top to bottom White matter -> contains the axons and neurons Gray matter -> lacks axons and neurons Basal nuclei (ganglia) -> collection of nuclei
Ventricles -> gaps or holes, cavities Limbic system -> group of structures in brain associated with emotions & drives Divisions of the Spinal Cord: Has many nerves running down the column Cervical nerves -> there are 8 pairs of them, connect to the neck, shoulders, arms & hands Thoracic nerves -> there are 12 pairs of them, connect to the shoulders, chest, upper abdominal wall Lumbar nerves -> there are 5 pairs of them, connect to the lower abdominal wall, hips and legs Sacral nerves -> 5 pairs of them, connected to the genitals and lower digestive track Coccygeal nerves -> 1 pair If a nerve is cut or damaged, it may impair the motor in a specific part of the body Spinal cord anatomy: Gray matter is surrounded by white matter Dorsal horn -> back of spinal Dorsal root -> afferent information Ventral horn -> from of spinal Cranial nerves: Enter & exit from the brain 10 attached to brainstem 2 are attached to other part of brain Olfactory nerve transmits info about smell Optic nerve transmits info about sight Early development of the nervous system: 1. Ovum (fertilized egg) develops into ball of cells which develops into a blastocyst -> week 1 2. The inner cells mass of the blastocyst has specializations -> week 2
3. The embryonic disk appears in the blastocyst -> week 3 4. The neural plate develops -> week 3 5. The neural groove develops from the neural plate -> week 3 6. The neural tube develops, which becomes part of the CNS and a part of PNS
7. Vesicles begin to develop in the neural tube during week 4. The tube gets hollower and hollower. 8. The neural tube becomes the CNS o o o o Forebrain develops into the cerebral cortex and thalamus Midbrain develops into the midbrain Hindbrain develops into the cerebellum, pons and medulla The remaining cavity becomes the spinal cord, the ventricles and central canal Cerebral Spinal Fluid (CSF): Ventricle contains 150 ml of CSF Lateral ventricles, Third and fourth ventricles
The CSF is produced by the choroid plexus -> in the fourth ventricle but mainly in the two lateral ones Produces 500 ml/day The functions of the CSF: 1. Supports and cushions the central nervous system, gravity of the CSF and the brain are equal 2. Provides nourishment to the brain 3. Removes metabolic waste through absorption at the arachnoid villi (dumps into the venous blood supply) The CSF contains glucose It's colorless and acellular fluid, sterile It's circulated passively = not pumped It's secreted through choroid plexus and moves through the ventricles CSF Circulation: The ventricles are connected by the Foramen of Monro -> two connections from lateral to third ventricle In third ventricles the CSF flows through the cerebral aqueduct (goes through midbrain) into the fourth (sits between cerebellum and brain stem). The CSF then goes through the central canal The CSF leaves the interior cavities of sub canals to the outside of the brain -> subarachnoid space It leaves through openings at the bottom of fourth ventricle and enters subarachnoid space. 3 openings: foramens of lushka (2 lateral) and magendie The CSF works its way around brain and enters the arachnoid villi -> organelles, tissues, that transport CSF out of central nervous system and into the Dural sinus that connects to venous blood supply. Hydrocephalus -> increased pressure inside central nervous system; occurs with increase in CSF which doesn't leave, putting pressure on the brain o Communicating hydrocephalus -> problem with subarachnoid space or uptake of CSF in Dural sinus, bad communication between the ventricles, outside of ventricles
o Non-communicating hydrocephalus -> blockage with ventricles, inside the ventricles 3 Meninges (membranes) of the CNS 3 layers cover brain & spinal cord Skin -> Bone -> Meninges Dura mater -> covering central nervous system, thick Arachnoid membrane -> below Dura Pia mater -> at the bottom, thin, stuck to cerebral cortex/gray matter (outside of brain) Subarachnoid space-> between the arachnoid membrane and pia mater, made by arachnoid membrane, has legs like trabeculae sticking out to give support Dural (venous) sinus -> opening where the Dura opens up in the midline, where CSF is dumped CSF flows through arachnoid villi into the Dural sinus where it enters the blood supply and gets mixed in it and return to heart Blood Supply to the Brain The brain needs a consistent supply of glucose (doesn't require insulin) & oxygen Neurons are unable to store glucose in the brain, yet glucose is the only substrate that the brain can metabolize Lack of blood supply into the brain can cause interruptions & loss of consciousness or even stroke Brain receives 15% of blood supply The arteries transport blood into the brain (away from heart)
The common carotid artery splits into the external and internal carotid arteries The external carotid artery is outside of the head while the internal carotid artery is at the base of the brain. The vertebral artery is a small artery that comes through the spinal vertebral bone
Basilar artery -> made when the vertebral arteries from both sides come together at the base of the brain Circle of Willis -> safety check, if internal carotid doesn't work then it takes the blood from the one side and shoves it to another to continue the supply of the brain Brain edema -> when there is so much pressure in the cranium that it pushes the brain out of the skull, compresses the brain stem and cranial nerves Summary of Cerebral Circulation: CSF and Blood: 1. The choroid plexus produces the CSF which is transported around brain in ventricles. 2. The ventricles eventually lead into the subarachnoid space, where with the help of arachnoid villi, the CSF is transported into the Dural sinus which is connected to the venous system. 3. The blood is pumped from the heart into the carotid arteries and the vertebral arteries. 4. The vertebral arteries combine to form the basilar artery. 5. The carotid arteries split into internal and external 6. The carotid arteries and the basilar artery combine to form the circle of Willis which transports blood throughout the brain.
Blood-brain barrier (capillary wall) Basically the lining of the capillary wall The endothelial cells are close in place and they surround the capillary wall Things that may pass endothelial cell: o Water o CO2 o O2 o Lipid-Soluble substances o Ions like Na+, K+ & Cl- might have some difficulty o Drugs must cross to reach target: Nicotine Caffeine Alcohol Morphine (not easily) Heroine (modified morphine) Large plasma proteins need help to cross Active transport of glucose and some amino acids There is also blood-csf barrier (choroid plexus) Astrocytes (glial cells) -> surrounding neurons, provide structural support, speak to capillaries, regulate extracellular environment, kind of attached to capillary & neuron, regulates exchange between blood and neurons