Central Nervous System
1
Intro
The central nervous system consists of the brain and spinal cord:
Myelinated neurons form the white matter in the inner region of some areas of the brain and the outer area of the spinal cord.
Unmyelinated neurons form the grey matter around the outside areas of the brain and forms the H-spaced core of the spinal cord. Damage to grey matter is usually permanent.
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Chapter 8: The Nervous System and Homeostasis
ection 8.3
grey matter in the cortex of the brain (outside) Grey matter does not repair itself- it could take a lifetime so its protected in the middle of the spinal cord -spinal cord injury could leave to paralysis since it takes so long to heal
The Brain: Overview
The human brain comprises three distinct regions:
The forebrain contains paired olfactory lobes and the cerebrum.
The midbrain is less developed and acts as relay centre for some eye and ear reflexes.
The hindbrain contains the cerebellum, pons, and medulla oblongata.
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100 billion neurons in the brain -olfactory is a fancy word to describe how we process scent information- how we smell- helps detect smells as well as flavours (we actually taste with our scent as well as with our taste buds)
cerebrum is what you think of when you think of the folds, bumps and grooves of the brain- makes up the biggest mass- can further break this down and talk about the 4 different lobes midbrain is a relay center for sensory information
hindbrain near the brain stem- the lowest part
brain is very important- plays a key role in homeostasis and needs protecting -it is a fragile gelatinous structure Three layers of meninges are very thin layer but very toughlastic/e to enclose and protect our brain Clear cerebrospinal fluid instead of blood flowing in our brain- bathes the entire brain - shock absorber if you were to fall down and cushions the brain from injury Blood-brain- barrier- blood vessels do exist within layers but do not actually extend into the brain tissue- this barrier keeps blood separate from the nervous system- components of the blood that are useful like oxygen and glucose are needed from the blood so they can pass through this barrier but the BBB is gonna protect the brain from other things entering. The junctions or spaces between this barrier are very tight therefore not allowing many substances to enter in the brain. This is one of the challenges of treating neurological disorders because many medications cannot pass the BBB- this is an active field of study to try to study medications that can cross the BBB to see what effects it has on human health SOME THINGS DO CROSS the BBB- nicotine, alcohol & caffeine- and these substances has a rapid effect on the brain.
The brain is protected by the skull, meninges, cerebrospinal fluid, and the blood brain barrier.
Meninges are three layers of tough, elastic tissue.
Cerebrospinal fluid carries hormones, white blood cells, and nutrients, and acts a shock absorber.
Blood-brain barrier separates the blood from the CNS and selectively controls the entrance of substances into the brain from the blood.
The Hindbrain: Coordination and Homeostasis
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Chapter 8: The Nervous System and Homeostasis
Section 8.3
A – Cerebellum “little brain”: walnut shaped structure involved in unconscious coordination of posture, reflexes, body movement, and fine voluntary motor skills
Receives sensory information from receptors, located in joints and skeletal muscles; from balance receptors in the inner ear; and from receptors of touch, vision and hearing.
A,B & C
hind brain is an evolutionary structure that we always see in anything that resembles a brain -it has basic operations of keeping us alive ex. digesting, keeping balance, heart beating -cerebellum ex. reaching up and changing a lightbulb coordinating the motion in the right sequence of events to keep us in balance and keep us in posture
The Hindbrain: Coordination and Homeostasis
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Chapter 8: The Nervous System and Homeostasis
Section 8.3
B – Medulla Oblongata: connect the brain and spinal cord at the base of the brainstem; coordinates many reflexes and automatic bodily functions that maintain homeostasis, including heart rate, constriction and dilation of blood vessels, coughing and rate and depth of breathing
C – Pons: mass of fibres in the brainstem; relay centre between right and left halves of the cerebrum and cerebellum
Medulla Oblongata- extension of the brainstem - where the spinal cord connects with the brain -also responsible for coordination and things that are automatic No higher order thinking making sure we are basically living - vital functions and staying in homeostasis Ex. Chicken head cut off - MO was still in tact so it could stay alive (18 months) PONS read slide FUN FACT= Pons not working can = sleep paralysis - when you are dreaming the pons will prevent you from acting out your dreams by shutting off your ability to move around
Normally what happens when you begin to wake up the pons will relay information and coordinate everything, but if its not working properly and doesn’t turn back on when you begin to wake up, a person can be awake, still be dreaming, and not actually be able to move their body.
Pons= out of sync but usually adjusts itself within a few seconds- minutes
Before we move on- Note- lots of overlap between functions of the brain We know that the brain has plasticity/ flexibility to change the way it does a function if it needs to if one part of the brain isn’t functioning properly it is possible that other parts of the brain can pick up on that function and do it - don’t get the idea that one part of the brain only does ONE thing because the brain is very adaptable
Midbrain: Processing Sensory Input
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Chapter 8: The Nervous System and Homeostasis
Section 8.3
D – Midbrain: found above the pons; involved in processing information from sensory neurons in the eyes, ears, and nose
It relays visual and auditory information between hindbrain and forebrain; controls skeletal muscle movement and plays an important role in eye movement.
sensory processing- taking in information from eyes, ears, nose etc. -takes in this information from the sensory receptors to help us generate an awareness of our environment- but doesn’t really give us explicit sensations that we have of smell/ vision- these higher order things will happen more in the cerebrum.
ex. Vision- we will take in the information from our eyes and send it it to the back of the cerebrum where images are formed (occipital lobe). It also provides us with a 3D map of our environment - if you ever try to close your eyes and navigate around a room its much harder without your sight, but you might still be able to picture where things are in the room and may even be able to navigate around them without actually seeing them = this is sensing the 3D environment that happens in the midbrain
Forebrain: Thought, Learning, and Emotion
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Section 8.3
E – Thalamus “the great relay station”: sits at the base of forebrain; provides connections between the forebrain and the hindbrain; receives sensory information and relays it to the appropriate region of the cerebrum
F- Hypothalamus: lies just below thalamus
Regulates the body’s internal environment (blood pressure, heart rate, body temperature, thirst/hunger, and emotions (fear, anger, pleasure)
Connects the nervous system to the endocrine system- (coordinates the pituitary gland)
Thalamus receives information from the hindbrain as well as sensory information (minus the sense of smell) and relays it to the appropriate region in the cerebrum hypothalamus (below thalamus) is a connection between the endocrine system & nervous system - Main job is to keep our body in homeostasis, similar to MO, but is going to do this by releasing hormones that will interact with the pituitary glands which will then send out its own hormones FUN FACT- Brain damage or a tumour that affects the hypothalamus can cause a person to display unusual, even violent behaviour.
Forebrain: Thought, Learning, and Emotion
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Chapter 8: The Nervous System and Homeostasis
Section 8.3
G – Cerebrum:
largest part of brain (4/5ths of mass)
divided into right and left cerebral hemispheres, which each contain centers for intellect, learning, memory, consciousness, and language- interprets and control responses to sensory information.
cerebrum - the “primate brain” - disproportionately large cerebrum - why we have the ability to do things that many organisms can’t because of the cerebrum - ex. higher-order, more complex skills, learning, fine motor skills, memory -cerebrum is separated into the left and right hemispheres- a structure in the middle (corpus collosum) allows these sides to communicate with one another -The lateral ventricle produces cerebrospinal fluid which transports hormones, white blood cells, and nutrients across the blood-brain barrier for cells of the brain and spinal cord. It also circulates between the layers of the meninges
The Structure and Function of the Cerebrum
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Chapter 8: The Nervous System and Homeostasis
Section 8.3
Each half (hemisphere) of the cerebrum contains a mass of white matter and a thin, outer covering of grey matter called the cerebral cortex.
Cognitive functions originate from both right
hemisphere and left hemisphere components.
However, some functions have a dominant
hemisphere:
the right-brain is associated with holistic and intuitive thinking, visual-spatial skills, and artistic abilities
the left-brain is associated with sequential and logical ways of thinking, and linguistic/mathematical skills
The left and right cerebral hemispheres are linked by the corpus callosum, which sends information from one hemisphere to another.
visual spatial skills- the ability to look at an object, notice the difference between objects, have depth perception *now this is pretty old school thinking
The Cerebral Cortex
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Section 8.3
Each hemisphere can be divided into FOUR pairs of lobes:
frontal lobes: integrates information from other parts of the brain and controls reasoning, critical thinking, memory, personality, and precise fine motor skills. One area of the frontal lobe is associated with motor speech (Broca’s area). Primary Motor Area: Each side of the frontal lobes controls muscles on the opposite side of the body
2.parietal lobes: receive and process sensory information from the skin. Processes information about body position and orientation. Primary Somatosensory Area: receives sensory information from left & right side of the body
Speech is very complex- only the motor production of speech is involved in Broca’s area - if there is damage in this area of the brain- someone can still understand language and can still form them in their mind, but they can not produce the muscles involved in making the sounds of speech- a DIFFERENT area of the brain is responsible for understanding speech
Primary motor area: a band of tissue that runs down the right and left hemisphere- a band of neurons that sends motor messages to control muscles on the opposite side of the body
Primary motor area & Primary Somatosensory area work together
Somatosensory and Motor Cortex
The proportion of brain space devoted to a particular part of the body is related to the importance of sensory information and complexity of movement in that body structure.
brain map sensory information & motor output
The Cerebral Cortex
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Chapter 8: The Nervous System and Homeostasis
Section 8.3
3. occipital lobes: receive and analyze visual information. Needed for recognition of visual information.
4. temporal lobes: share some visual processing but mainly process auditory information. Important in understanding speech and retrieving visual and verbal memories.
Temporal lobe -some visual processing but mainly auditory -makes sense based on location of brain area to receive the information Wernickes area - works with Broca’s area -not only to generate speech and make sound (Broca’s area) but to understand *damage to wernickes area would allow people to make sounds but the way that they would string syllables together wouldnt make sense because their understanding of language would be impaired