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RESPONDING TO THE ENVIRONMENT- HUMANS Nervous system (nerves) Endocrine system (hormones) Human nervous system Need for a nervous system: Reaction to stimuli (changes in the environment- external and internal) Coordination of the various activities of the body Examples of responses Voluntary actions Eating a cake Riding a bicycle Walking Involuntary actions - Your heart beat - Breathing - Removing hand from hot object Playing the piano - Choking Coming to school - Salivating - Blinking Central nervous system Brain + Spinal cord Protected by: Meninges (3 membranes) Skeleton (bone) Cerebrospinal fluid Homework: Draw a labelled diagram of the section of the brain, and annotate with the functions.(only cerebrum, cerebellum, corpus callosum, Medulla oblongata and spinal cord pg 188 without the skull etc. NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM 12 pairs cranial nerves 31 pairs spinal nerves CENTRAL NERVOUS SYSTEM (CNS) Brain + Spinal cord MOTOR NERVES Conduct impulses from the CNS to the effectors AUTONOMIC NERVOUS SYSTEM Conducts impulses from the CNS to the involuntary muscles (smooth muscles and heart muscles) and certain glands SYMPATHETIC DIVISION Prepares the body for action, ‘fight or flight’ SENSORY NERVES Conduct impulses from the receptors to the CNS SOMATIC NERVOUS SYSTEM Conducts impulses from the CNS to the voluntary muscles PARASYMPATHETIC DIVISION Enables body to return to normal Cranial+spinal Sympathetic branch 1. Increases heart rate Parasympathetic branch 1. Decreases heart rate 2. Relaxes walls of bladder 3. Dilates pupils 2. Contracts wall of bladder 3. Constricts pupils 4. Constricts many arteries 5. Increases blood pressure 4. Dilates arteries 5. Decreases blood pressure Brain structure Cerebrum Corpus Callosum cerebellum hypothalamus Spinal cord Pituitary gland medulla brain functions state the functions of each of the following parts of sensory and motor neurons: nucleus, cell body, cytoplasm, myelin sheath, axon and dendrites. Reflex action: quick, automatic response to a stimulus. Reflex arc: The nerve pathway taken in a reflex action A reflex arc Reflex arc Stimulus → receptor (converted to impulse) → sensory nerve → Spinal cord (via dorsal root) → synapse → interneuron → synapse → (via ventral root) motor neuron → effector The knee jerk reflex action Sometimes called a relay or Connector neurone Another reflex action Significance of a reflex action Protects the body from further damage by reacting quickly (from spinal cord not brain) Disorders of the CNS Alzheimer’s disease Ex 3 pg 204 (only 10 marks) Multiple sclerosis Ex 4 pg 206 (only 10 marks) (focus is on causes and symptoms) Significance of synapses It allows messages to be passed from one neuron to the next. Allows impulses to travel in one direction only. Allows nerves to join or split (1 → many or many→1) Removes continual background stimuli. Consequences of brain and spinal injury Brain injury pg 208 Spinal injury pg 210 Also stem cells research has potential to repair damage Negative effects of drugs on the central nervous system Slows down reaction time, causes loss of self control + even coma Loss of memory May damage the brain Receptors the body responds to a variety of different stimuli, such as light, sound, touch, temperature, pressure, pain and chemicals (taste and smell). receptors, neurons and effectors function together in responding to the environment. Human eye Draw a section of the human eye, provide all labels and functions. (pg 221) Binocular vision 2 eyes Use of two eyes with overlapping fields of vision. It allows interpretation in 3D Structure and function Allows the front of the eye to keep its bulging shape. Yellow spot – has rods and cones that allows one to see fine detail Separates the cornea from the lens. Sends light vibrations to the visual cortex in the cerebrum Focuses the image on the retina. Light passes through it The optic nerve leaves the eye, no light sensitive nerves available Controls the size of the pupil Allows the lens to change shape during focusing Together with the lens focuses the image on the retina Image formation Light reflected from objects passes through the cornea, aqueous humour, pupil, lens and vitreous humour and falls on the retina where an image is formed. All the structures named above but pupil bring about refraction such that the image is focused on the retina Bending light (refractions) Structure responsible for refraction are the cornea and lens. Rods and cones pick up the images accordingly as per their specific adaptations. In this way light stimulus is converted into a nerve impulse on the retina. These impulses are converted to the optic nerve to the cerebrum to be interpreted. Accommodation Refers to the ability of the eye to change the shape (convexity) of the lens to ensure a clear image is formed on the retina whether the image is near or distant. Near vision (<6m away) (summarised pg 225 textbook) • the cilliary muscles contract •the sclera is pulled forward • the suspensory ligaments slacken • the tension on the lens decreases • the lens becomes more convex • the refractive power of the lens increases • a clear image is formed on the retina Distant vision (>6 m away) Ciliary muscles relax Sclera goes back to normal position Suspensory ligaments become taut Tension on the lens increases The lens becomes less convex The refractive power of the lens decreases The clear image is formed on the retina Changing lens thickness The lens is slightly elastic, its relaxed state is short and fat. Cilary muscles are attached to the lens, when contracted they pull the lens thin Pupil reflex/ pupillary mechanism Your eye can be damaged by harsh light. Your iris controls light allowed into the eye by changing the size of the pupil In bright light The circular muscles of the iris contract The radial muscles relax The pupil constricts The amount of light entering the eye is reduced In dim light The radial muscles of the iris contracts The circular muscles relax The pupil dilates The amount of light entering the eye is increased Adaptation of the eye The sclera is tough and non-elastic to protect the inner structures of the eye. The cornea is transparent allowing light to enter the eye. The choroid has a brown pigment which absorbs the light thus preventing reflection of light within the eye. The iris has circular and radial muscles which alter the size of the pupil. The ciliary muscles help to change the shape of the lens for accommodation The suspensory ligaments holds the lens in position The lens can refract the light to focus clearly on the retina The retina has rods and cones, to receive the stimulus of light The aqueous humor maintains the shape of the eye, supplies the eye with oxygen and nutrients and plays a minor role in the refraction of light. Visual defects Short-sightedness Causes: Eyeball being too long Inability of the lens of the eye to become less convex (rounded). Treatment Wear glasses with a concave lens. Contact lenses Laser treatment. Long-sightedness (farsightedness) Causes Eyeball being too rounded Inability of the lens to become more convex – common in the elderly Treatment Wear glasses with convex lens Astigmatisation The front surface of the cornea is curved more in one direction than \in the other. Symptoms: Distortion or blurring of images at all distances Headache and fatigue squinting and eye discomfort and irritation Treatment Prescription glasses are required if the degree of astigmatisation is great enough to cause eye strain and head ache, or distortion of vision. Cataracts Refers to: The cloudy, opaque part of the lens. not clear understanding of its causes. Treatment: Surgical removal of the lens. replacing the lens with a synthetic lens. VISION WITH A CATARACT The ear Draw label and give functions -:- pg 229(you should be used to this by now so don’t complain) Main functioning of the ear Hearing balance Structure and function The ear consists of three regions: Outer ear Middle ear Inner ear Oval window Round window Hearing Path of sound Sound waves → Pinna →auditory canal →tympanic membrane (vibrates) →hammer →anvil →stirrup →oval window → fluid of the cochlea (as pressure waves) →organ of Corti coverts stimuli to impulses → auditory nerve→ brain (cerebrum) Adaptations Pinna --- large and traps sound waves Cerumen (wax) and hairs --- prevents small organisms from entering the ear Cerumen --- prevents the tympanic membrane from drying out Hammer --- transmits vibrations from the eardrum to the anvil then stirrup. Stirrup transmits vibrations to the oval window into the inner ear The Eustachean tube allows air to move in and out of the middle ear, thus maintaining equal pressure on either side of the ear drum Amplificication Decreasing size of structures as you move to inner ear causes amplification. Balance The ear is responsible for balance in the following ways: 1. The cristae in the semicircular canals are stimulated by changes in the direction and speed of movement 2. The maculae in the sacculus and utriculus are stimulated by changes in the position of the head When stimulated, the cristae and maculae convert the stimuli received into nerve impulses. The nerve impulses are transported along the auditory nerve (vestibular branch) to the cerebellum to be interpreted. The cerebellum then sends impulses to the muscles to restore balance. Hearing defects Middle ear infection Cause: Excess fluid in the middle ear caused by pathogen infection. Treatment: Inserting grommets Antibiotics Deafness Cause: • Injury to parts of the ear, nerves or parts of brain responsible for hearing. Hardened wax Hardening of ear tissues (e.g.ossicles). Treatment: Hearing aids Cochlear implants Hearing aids Cochlear implants