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Human Biology Chemical Messengers Essay

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Human Biology 3A Notes CHAPTER 4: Chemical Messengers Homeostasis:the maintenance of a constant internal environment Homeostasis ensures that the fluid environment of the cells: • Contains the optimum concentration of nutrients, ions, gases and water • Stays at a constant temperature – the optimum temperature for normal cell functioning • Is maintained at the optimum pressure Feedback system: Negative feedback system: Negative feedback: Positive feedback:

A situation where the response toa stimulus changes the original stimulus Where the response to a stimulus brings about a change opposite to, or reduces the effect of, the original stimulus Feedback that brings about a change opposite to, or reduces the effect of, the original stimulus Feedback that reinforces the original stimulus Common features of a negative feedback system: Example: ?Stimulus: ? Receptor: ? Modulator: the change in environment that causes the system to operate detects the change control center (brain) that processes information from receptor and sends to the effector ?

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Effector:carries out a response counteracting the effect of the stimulus ? Response:a response is carried out (action) ? Feedback:is achieved because the original stimulus has been changed by theresponse Homeostatic mechanisms are controlled by both the nervous system and the endocrine system.

Nervous system:sends electrical messages to appropriate organs Endocrine system:secrete chemical messengers Endocrine system is generally slower Endocrine system: Exocrine glands: Endocrine glands: he body system involved in chemical communication between cells; made up of endocrine glands secrete into a duct that carries the secretion to the body surface or to one of the body cavities secrete hormones into the extracellular fluid that surrounds the cells making up the gland Hormone:a chemical secreted by an endocrine gland and often carried in the blood that affects the functioning of a cell or organ Steroid hormones:work by entering target cells and combining with a receptor protein inside the cell.

Human Biology 3A Notes

CHAPTER 5: The Central Nervous System Jennifer Nguyen The nervous system is the communication network and control centre of the body. The nervous system is also involved in maintaining homeostasis. The nervous system is divided into two parts: The central nervous system: •Consists of the brain and spinal cord •The control centre for the whole nervous system The peripheral nervous system: •Made up of nerves that connect the central nervous system with the receptors, muscles and glands Protection of the Central Nervous System Structures that protect the CNS: Bones •Cerebrospinal fluid (CSF) •Membranes called meninges Cranium: Vertebral canal:the opening in the vertebrae through which the spinal cord part of the skull that houses and protects the brain passes Meninges:membranes covering the brain and spinal cord (i. e. the entire CNS). The meninges is made up of three layers 1. Outer meningal layer (dura mater): closest to the skull, tough and fibrous, similar texture to a rubber glove 2. Middle meningal layer (arachnoid mater): lose mesh of fibres with a web-like appearance; provides a cushioning effect 3.

Inner meningal layer (pia mater): firmly adheres to the brain and spinal cord; very delicate and contains blood vessels Cerebrospinal fluid: •Fluids produced in the cavities of the brain •Fills the brain cavities and surrounds the brain and spinal cord •Contains few cells, glucose, protein, urea, salts •Acts as a shock absorber, cushioning any blows or shocks the CNS must sustain •CSF is formed from blood that circulates around and through the CNS and eventually re-entering blood capillaries. During irculation, takes nutrients to brain and spinal cord and carries away wastes •Brain floats in the cranium, supported by CSF Therefore the cerebrospinal fluid protects, supports and transports. THE BRAIN THE CEREBRUM •Largest part of the brain •Made up of left and right hemispheres •Consists of outer surface of grey matter 2 – 4mm thick, known as the cerebral cortex •Below the cortex there is white matter and deep inside the cerebrum there is additional grey matter called the basal ganglia. Basal ganglia: White matter: Grey matter: Cerebral cortex asses of grey matter inside each cerebral hemisphere the part of the brain and spinal cord made up of myelinated fibres the part of the brain and spinal cord made up of unmyelinated fibres •Cerebral cortex is folded creating round ridges called convolutions to increase the surface area •Convolutions are separated by shallow downfolds (sulci) or deep downfolds (fissures) The longitudinal fissure (the deepest fissure) almost separates the cerebrum into 2 halves: the left and right cerebral hemispheres. The cerebral hemisphere is divided into four lobes: the frontal, temporal, occipital and parietal lobes.

Another part of the cerebrum, the insula, deep inside the brain is regarded as a 5th lobe. In between the cerebral cortex and basal ganglia is white matter composed of bundles of myelinated fibres called tracts There are three types: •Tracts that connect various areas of the cortex within the same hemisphere •Tracts that carry impulses between the left and right hemispheres •Tracts that connect the cortex to other parts of the brain and spinal cord The three main parts of the cerebrum: cerebral cortex, basal ganglia, and tracts Functions of the cerebrum: Involved in mental activities such as thinking, reasoning, learning, memory, intelligence and sense of responsibility There are three types of functional areas in the cortex: •Sensory areas: interpret impulses from receptors •Motor areas: control muscular movements •Association areas: concerned with intellectual and emotional processes The basal ganglia consist of groups of nerve cell bodies associated with control of skeletal muscles. Two cerebral hemispheres are not identical. Right-handed people have wider right frontal lobes and wider left occipital and parietal lobes.

A very important function of the cerebrum is memory: •Association areas of the cerebral cortex are involved in memory •Memory is stored in pathways of nerve cells •When a memory is stored, new links are made between neurons or existing links are made THE CEREBELLUM •Lies under the rear part of the cerebrum •Second largest part of the brain •Folded into a series of parallel ridges •Outer folded part = grey matter •Inside is white matter branching to all parts of the cerebellum Functions of the cerebellum: Exercises control over posture, balance and fine co-ordination of voluntary muscle movement •To carry out these functions, it receives sensory information from inner ear and from stretch receptors in the skeletal muscles •Functions of the cerebellum take place below the conscious level •Impulses do not originate in the cerebellum so without it, we would still be able to move but movements would be spasmodic, jerky and uncontrolled THE HYPOTHALAMUS •Lies in the middle of the brain; cannot be seen from the outside •Controls many body activities but is mainly concerned with homeostasis Functions of the hypothalamus: The autonomic nervous system •Body temperature •Food and water intake •Patterns of waking and sleeping •The contraction of the urinary bladder •Emotional responses •Secretion of hormones and coordination of parts of the endocrine system THE MEDULLA OBLONGATA •A continuation of the spinal cord, about 3 cm long Contains: •The cardiac centre: regulates the rate and force of heartbeat •Respiratory centres: control rate and depth of breathing •The vasomotor centre: regulates the diameter of blood vessels Function: Regulates reflexes of swallowing, sneezing, coughing and vomiting THE SPINAL CORD Spinal cord: a roughly cylindrical structure that extends from the foramen magnum to the second lumbar vertebram – about 44cm long Foramen magnum: large opening at the base of the skull Second lumbar vertebram: about waist level •Spinal cord is enclosed in the vertebral canal •Inside the ring of bone is three meningal layers •Grey matter in the spinal cord is in the centre and is surrounded by white matter (opposite of brain) • • The grey matter is roughly in the shape of a “H” In the crossbar of the H is a small space called the central canal This runs the length of the spinal cord and contains cerebrospinal fluid Myelinated fibres of the white matter are arranged in bundles known as ascending and descending tracts. Ascending tracts:are sensory axons that carry impulses upwards towards the brain Descending tracts:contain motor axons that conduct impulses downwards, away from the brain Functions of the spinal cord: . To carry sensory impulses up to the brain and motor impulses down from the brain 2. To integrate certain reflexes (fast, automatic responses) Control of movement The intention to contract muscles begins in the motor association are of the cerebral cortex. Motor association area: the part of the cerebrum where behaviour is planned; nerve in this area plan the sequence and amount of muscle contraction required for actions like walking, riding or speaking.

Primary motor area: an area of the cerebral cortex that sends out nerve impulses to cause muscle contractions. Intention to contract muscle? motor association area? primary motor area ? lower centres in the brain? spinal cord? resulting in the contraction of muscle Parts of the body that have more muscles have more neurons eg: hands Upper body neurons: carry nerve impulses away from the motor area in the cerebral cortex.

These neurons connect the brain to the appropriate level in the spinal cord. Lower motor neurons: carry impulses to the muscles. Role of the cerebellum: The cerebellum receives nerve impulses from the cerebrum through the upper motor neurons. •Receives information from the eyes, ears and stretch receptors from muscles and joints •It assesses the conscious desire to move along with the information about the position of the body and state of the muscles Balance

The cerebellum must receive constant input from the senses and make constant adjustment to the muscles in order to maintain balance. The cerebellum receive input from: •The cerebrum, which gives information about conscious awareness of the position of the body •The semicircular canals in the ear which give information about movements if the head •The saccute and utricle, two chamber in the ear, which give information about the relative amounts of pressure and joints which report on body movements and joint positions

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Human Biology Chemical Messengers Essay. (2016, Oct 24). Retrieved from https://graduateway.com/human-biology-chemical-messengers

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