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The Nervous System AP Biology

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Presentation on theme: "The Nervous System AP Biology"— Presentation transcript:

1 The Nervous System AP Biology

2 The Nervous System Function: environment is constantly changing – nervous system detects those changes and helps the organism respond/adapt Irritability: ability to respond to a stimulus

3 The Nervous System Nervous System detects (sensory input), processes (integration), and responds (motor output) Peripheral Nervous System detects and responds Central Nervous System processes information


5 The Neuron (Nerve Cell)
Three types of neurons: Sensory – carry impulses from the sense organs (receptors) to the CNS Motor – carry impulses from the CNS to the muscles or glands (effectors) Interneurons – connect and carry impulses between sensory and motor neurons

6 Three components of Neurons
Cell body – largest part; most metabolic activities take place here; contains nucleus Dendrites – carry impulses from the environment or other neurons toward the cell body

7 Three components of Neurons
Axon – long fiber that carries impulses away from the cell body Terminal branches – branching of axon Synaptic knobs – ends of axon; contain vesicles with neurotransmitters


9 The Nerve Impulse Resting potential – a nerve cell has an electric potential because OPPOSITELY charged ions are on each side of the membrane Anions are mainly on the inside of the the cell; cations on the outside

10 The Nerve Impulse Ungated ion channels allow ions to diffuse across the plasma membrane These channels are always open This diffusion does not achieve an equilibrium since sodium-potassium pumps transport these ions against their gradients

11 Hyperpolarization Gated K+ channels open  K+ diffuses out of the cell  the membrane potential becomes more negative

12 Depolarization Gated Na+ channels open  Na+ diffuses into the cell  the membrane potential becomes less negative

13 The Nerve Impulse Action Potential – a rush of Na+ flow into the membrane causing an imbalance in the charge on each side of the membrane This causes the POLARITY to shift and a wave (impulse) moves down the length of the neuron +



16 Step 1: Resting State

17 Step 2: Threshold

18 Step 3: Depolarization

19 Step 4: Repolarizing

20 Step 5: Undershoot

21 Na+ gates close & K+ gates open
K+ gates close Na+ gates open Stimulus

22 During hyperpolarization or undershoot, Na+ channels are closed
Neuron cannot depolarize in response to another stimulus: refractory period The refractory period assures impulse conduction is unidirectional


24 Myelin Is composed of 80% lipid and 20% protein
Used for insulation and to help speed up the nerve impulse Wraps around the axon of some neurons

25 Myelin Gaps in myelin sheath cells called Nodes of Ranvier – allow impulses to move more quickly down neurons

26 Myelin In Saltatory Conduction, only the Nodes of Ranvier depolarize and therefore conduct an impulse faster

27 The Synapse SYNAPSE: the space between the axon of one neuron and the dendrite of another Axon terminals have vesicles containing chemicals: NEUROTRANSMITTERS These chemicals are secreted from the axon of one neuron  stimulates receptor sites on the effector or the dendrite of the next neuron

28 Neurotransmitter Action at Synapse
Action potential arrives at axon terminal of presynaptic neuron Synaptic vesicles rupture, releasing neurotransmitter into synapse Neurotransmitter diffuses across synapse & binds to receptor protein on postsynaptic cell Postsynaptic cell is excited or inhibited Neurotransmitter in synapse is deactivated



31 Nervous System Organization
Cnidaria - nerve net loose organization of bi-directional neurons no centralization Flatworms - ladder 2 anterior ganglia (rudimentary brain) with paired, longitudinal nerve cords paired sensory organs (eyespots)

32 Nervous System Organization
Segmented worms - advanced ladder prominent brain solid, fused, ventral nerve cord segmentally arranged ganglia

33 Nervous System Organization
Arthropods prominent brain solid, fused, ventral nerve cord extensive fusion of ganglia well-developed sensory organs exhibit complex behaviors

34 Organization of the NS The human nervous system is divided into 2 major divisions: Central Nervous System (CNS) Control center of body, brain and spinal cord Peripheral Nervous System (PNS) Nerves (bundles of axons)

35 CNS: Parts of the Brain Forebrain Midbrain Hindbrain

36 Hindbrain Cerebellum coordinates muscular movements Medulla oblongata
regulates heart rate, blood pressure and breathing contains reflex centers for vomiting, swallowing, sneezing, hiccupping, and coughing Pons helps regulate respiration

37 Forebrain Thalamus – switching station for sensory input for all senses but smell; relays sensory info to cerebrum and motor info from the cerebrum Hypothalamus – control hunger, thirst, fatigue, anger, and body temp; regulates pituitary gland


39 Forebrain Cerebrum – divided into left and right hemispheres
Corpus callosum – major connection between hemispheres Left hemisphere primarily responsible for right side of body; right hemisphere primarily responsible for left side

40 Forebrain Cerebral cortex – outer covering of gray matter
The more convoluted the surface, the more surface area, the more neurons

41 Forebrain Cerebrum – divided into frontal, temporal, parietal, and occipital lobes Frontal lobe Contains the primary motor cortex (controls actions of skeletal muscles) and olfactory cortex (smell)

42 Forebrain Parietal lobe
Contains the primary somatosensory cortex and gustatory cortex (taste) Temporal lobe Contains auditory cortex (sound) Occipital lobe Contains visual cortex (sight)

43 PNS Sensory – transmits impulses from the sense organs (such as the ears and taste buds) to the CNS Motor – transmits impulses from the CNS to the muscles or glands (somatic or autonomic)

44 Somatic – conscious movement of the body
Autonomic – regulates activities that are automatic or involuntary Sympathetic (stress, high energy) and Parasympathic (leisure, rest) are antagonistic systems that turn an autonomic response on or off



47 Sympathetic effects: dilates pupil accelerates heartbeat & respiration inhibits stomach & intestine activity relaxes urinary bladder Parasympathetic effects: constricts pupil slows heartbeat & respiration stimulates stomach & intestine activity contracts urinary bladder


49 Reflex Arc Some actions don’t/can’t wait for your brain to interpret the signal Reflexes are involuntary actions; they travel from ____ to ____: Receptors (nerve “endings”) Sensory neurons Interneurons Motor neurons Effectors (muscles or glands)



52 Types of Sensory Receptors
Thermoreceptors – detect heat and cold Pain receptors (nocioceptors) – detect chemicals released from injured cells Mechanoreceptors – detect mechanical energy (touch, pressure, vibration)

53 Types of Sensory Receptors
Chemoreceptors – detect chemicals Photoreceptors – detect light energy Electroreceptors – detect electrical fields

54 How are sounds sensed? The ear captures, transmits, and converts sound into electrical signals Ear has three basic parts: Outer ear Middle ear Inner ear

55 How are sounds sensed? Outer ear: external ear (pinna) and auditory canal Funnels sound Sound waves vibrate the tympanic membrane

56 How are sounds sensed? Middle ear Tympanic membrane (ear drum)
Three tiny bones: malleus (hammer), incus (anvil), stapes (stirrup); transfer vibrations to the oval window on the cochlea Eustachian tube – equalize pressure; connects middle ear to pharynx

57 How are sounds sensed? Inner ear: cochlea
converts vibrations into electrical signals As the oval window vibrates, it sets the cochlear fluid in motion Moving fluid brushes over hairs Bending of hairs is sensed by mechanorecptors and sends the signal to the brain (auditory nerve)


59 Equilibrium Equilibrium is maintained by the semicircular canals

60 Equilibrium The semicircular canals are arranged in the X, Y, and Z planes Therefore, any movement in any direction will be perceived Fluid in the canals brushes over hairs Movement of hairs is sensed and the signal is sent to the brain


62 Equilibrium Dizziness can be due to the momentum of the fluid in the canals You’ve stopped moving, but the movement of the fluid in the semicircular canals makes you think you’re still moving

63 Fish “Hearing” – Lateral Lines
Contains mechanoreceptors that function similarly to mammalian inner ear Gives info about direction and velocity of water flowing over fish’s body

64 How is light sensed? Sclera – tough, white layer
Conjunctiva – external cover of sclera; keeps eye moist; conjuctivitis (pink eye)

65 How is light sensed? Cornea – transparent covering in front of eye
Choroid – thin, pigmented layer lining interior surface of the sclera; prevents light rays from scattering and distorting the image Iris regulates size of pupil/amount of light into eye

66 How is light sensed? Lens focuses light on retina
Retina – Contains photoreceptors (Except at the optic disk where the optic nerve attaches) Rods: Black and White Cones: Color Optic nerve takes electric signals from eye to brain

67 Rods and Cones ~ 125 million rod cells
Rod cells are light sensitive but do not distinguish colors ~ 6 million cone cells Not as light sensitive as rods but provide color vision Most highly concentrated on the fovea – area of retina lacking rods


69 Insects smell through their legs and antennae
How are scents sensed? Insects smell through their legs and antennae Male silkworm moth Bombyx mori Sensory hairs on antennae detect pheromones released by female

70 How are scents sensed? Olfactory nerves are stimulated when chemicals touch them Different chemicals create different responses in the olfactory nerves; hence we detect different smells


72 How are tastes sensed? Taste buds on tongue act just like the olfactory nerves Different chemicals stimulate the nerves in the taste buds differently; hence we detect different tastes Four “primary” tastes are bitter, sour, salty, and sweet


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