Nervous System and Neurotransmission
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- Created by: amazingemilyjones
- Created on: 16-04-19 20:24
Nervous System and Neurotransmission
Nervous System and Neurotransmission
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Why do we have a nervous system?
- Sensory input
- Monitors changes (stimuli) inside and outside the body
- Integration
- Processes and interprets sensory input to decide what should be done
- Motor output
- Supplies response by activating muscles or glands
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Central and Peripheral Nervous System
- Central nervous sytem:
- Brain: receives and processes sensory information, initiates responses, stores memories, generates thoughts and emotions
- Spinal cord: conducts signals to and from the brain, controls reflux activities
- Peripheral nervous system:
- Sensory neurons (sensory organs to spinal cord)
- Motor neurons (spinal cord to muscles and glands) with three subsets
- Somatic neurons
- Autonomic neurons (sympathetic and parasympathetic neurons)
- Enteric neurons (control gut activities)
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Divisions of the Nervous System
Neurons
- Pyrimidal neurons: largely found in the cerebral cortex, hippocampus, amygdala and corticospinal tract
- Grey matter = cell bodies, White matter = myelinated axons
Building Blocks of the Nervous System - Glia
- Oligodendrocytes (CNS)/Schwann cells (PNS)
- Produce myelin, facilitate transmission
- Astrocytes
- Enable homeostasis, physical barrier/connector
- Microglia
- Immune cells of the brain
- Phagocytose dead cells and debris
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The Brain
- Physiologically, the function of the brain is to exert centralised control over the other organs of the body
- Approximately 86 billion neurons in 1.4-1.6 kg
- Each neuron may receive up to 200,000 synapses - integration
- 2% of body mass
- Consumes 25% of energy (~500 calories a day)
- In all other vertebrates it consumes 10%
- ~95% is used for grey matter
- Grey matter = cell bodies
- White matter = myelinated axons
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Blood Supply to the Brain
- Blood flows to the brain via the internal carotid and vertebral arteries which join (anastomose) to form the Circle of WIllis
The Blood Brain Barrier
- Endothelial cells line the capillary walls with tight junctions between them
- Processes from astrocytes form a barrier around blood vesicles
- Prevents certain molecules entering from the blood stream
- Specific transporters allow certain molecules to access the brain
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Protecting the Brain
- The meninges are the membranes covering the brain and spinal cord
- Composed of dura mater, arachnoid membrane, pia mater
- Subarachnoid space (between arachnoid membrane and pia mater) is filled with cerebrospinal fluid (CSF)
- Meningitis = inflammation of meninges
Cerebrospinal Fluid (CSF)
- Secreted by the choroid plexus
- Buoyancy - holding up 1.4kg with CSF feels like 25g
- Protection from injury when jolted or hit
- Chemical stability and homeostasis: rinses the metabolic waste of the central nervous system through the blood-brain barrier
- Prevents ischemia (restricted blood supply = lack of oxygen)
- Exits into the venous sinuses via the arachnoid villi
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Cerebrospinal Fluid (CSF)
Anatomy of the Brain
Brain and Spinal Cord
- The spinal cord is where information comes into the central nervous system and directions are sent out
- Messages are then sent to and from the brain
- The spinal cord is divided into 31 segments, each gives rise to a pair of spinal nerves that supply a particular region of the body
Cranial Nerves
CNS vs. PNS
- Specific blood supply
- Blood brain barrier
- Different myelin producing cells
- Different immune defence - due to blood brain barrier
- High level of connectivity
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